UNIVERSITY    OF    CALIFORNIA    PUBLICATIONS 

IN 

AGRICULTURAL  SCIENCES 

Vol.  2,  No.  10,  pp.  297-314,  plate  53  March  5,  1925 


CHROMOSOME    NUMBER    AND    INDIVIDUALITY 
IN   THE   GENUS   CREPIS 

I.     A  COMPARATIVE  STUDY  OF  THE  CHROMOSOME 
NUMBER  AND  DIMENSIONS  OF  NINETEEN  SPECIES 

BY 

MARGARET  CAMPBELL  MANN 

(  Contribution  from  the  Division  of  Genetics,  University  of  California  ) 


Because  most  of  the  species  of  the  genus  Crepis  have  low  chromo- 
some numbers,  it  offers  obvious  advantages  for  the  study  of  comparative 
chromosome  relations.  The  chromosome  individuality  of  certain  species 
is  very  distinct,  so  much  so  that  it  could  be  used  as  a  diagnostic  character 
in  specific  determination.  These  facts  lead  to  an  inquiry  to  discover  first, 
whether  upon  careful  analysis  all  species  would  prove  to  differ  in  chromo- 
some individuality,  and  second,  what  relations  the  chromosome  groupings 
of  different  species  bear  to  one  another.  This  question  has  been  previously 
touched  upon  in  several  papers  by  Rosenberg  (1909,  1918,  1920)  and  in 
a  recent  contribution  by  Marchal  (1920).  Rosenberg  (1918)  called 
attention  to  the  fact  that  the  genus  Crepis  possesses  a  great  variety  of 
chromosome  numbers.  His  summary  showed  species  with  3,  4,  5,  8, 
9,  and  20  pairs.  In  order  to  determine  how  such  numerical  differences 
had  arisen  within  the  genus,  he  measured  the  chromosomes  of  a  three 
and  a  four-pair  species,  capillaris  (Reuteriana  of  Rosenberg)  and 
tectorum,  respectively,  and  found,  on  the  basis  of  measurements  of 
homotypic  anaphase  chromosomes,  that  three  of  the  chromosomes  of 
the  two  species  corresponded  accurately  in  size  and  that  the  fourth 
pair  of  tectorum  averaged  slightly  shorter  than  the  shortest  of  capillaris. 
He  noted  that  the  two  shortest  chromosomes  of  capillaris  often  mate 
later  than  the  other  two  in  p.  m.  c.  and  finds  associated  with  this  fact 
a  tendency  toward  lagging  and  irregular  division.     From  these  data  he 


298  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  2 

concluded  that  the  four-pair  species  have  arisen  from  a  three-pair  species 
by  the  fusion  of  two  gametes  each  of  which  has  received  an  extra  short 
chromosome.  Although  he  did  not  publish  measurements  on  the  two 
five-pair  species  which  he  studied  (rubra  and  multicaulis) ,  he  believed 
that  both  have  three  of  the  short  chromosomes,  and  that  these  types 
have  originated  by  a  repetition  of  the  process  which  gave  rise  to  the 
four-pair  types:  In  his  1920  contribution  he  changes  his  count  in  biennis 
from  twenty  to  twenty-one  pairs  and  concludes  that  it  represents  the 
three  chromosomes  of  capillaris  multiplied  fourteen  times. 

Marchal,  whose  work  was  done  without  knowledge  of  Rosenberg's 
paper,  expressed  (1920)  the  belief  that  four  is  the  ground  number  of  the 
genus  Crepis.  He  noted  that  p.m.c.  of  a  slightly  aberrant  capillaris  plant 
had  what  appeared  to  be  a  large  quadrivalent  multiple  chromosome 
plus  two  smaller  but  equal  elements,  and  that  most  of  the  species  of 
Crepis  seemed  to  have  four  pairs  of  chromosomes.  He  therefore  con- 
cluded that  capillaris  had  arisen  from  the  type  by  end-to-end  union 
between  two  chromosomes.  He  believed  that  the  differences  in  length 
which  had  been  noted  for  C.  lanceolata  platyphylla  (Tahara  and  Ishikawa, 
1911)  could  be  accounted  for  by  bipartition  of  one  chromosome  of  a 
species  with  four  pairs.  He  further  suggested  that  six-pair  species 
might  arise  by  doubling  of  the  three,  and  an  eight-pair  species  by 
doubling  of  the  four.  He  counted  sixteen  pairs  for  biennis  and  noted 
that,  while  the  individual  chromosomes  in  the  p.m.c.  of  this  species 
appeared  somewhat  smaller  than  those  of  certain  four-chromosome 
species,  the  total  mass  was  much  greater.  He  then  concluded  that 
biennis  is  an  eight-ploid  species. 


MATERIAL  AND  METHODS 

A  large  number  of  species  of  the  genus  Crepis  have  been  grown  and 
identified  in  the  greenhouse  of  the  Division  of  Genetics  of  the  University 
of  California  by  Professor  E.  B.  Babcock,  thus  making  it  possible  to  be 
certain  of  the  specific  determination  of  the  material  which  was  studied 
cytologically.  Since  the  chromosome  numbers  which  have  been  found 
to  characterize  the  species  thus  identified  differ  in  several  instances  from 
previously  published  counts,  the  data  are  presented  in  a  convenient 
form  in  table  1.  The  root  tips  were  fixed  in  chrom-acetic-urea  and 
stained  in  Heidenhain's  iron-haematoxylin.  In  most  species  the  reduced 
number  has  also  been  counted  by  Belling's  iron-aceto-carmine  method. 


1925]     Mann:  Chromosome  Number  and  Individuality  in  the  Genus  Crepis         299 


TABLE  1 

Chromosome  Counts  of  27  Species  of  Crepis 


Number 

Species 

N 

2N 

Author 

alpina  L 

4 
5 

10 
10 

Marchal  (1920)* 

Rosenberg  (1920)f 
Mann  (1922)J 

amplexifolia  Willk 

4 

8 

Mann 

aspera  L 

4 
4 

8 

Marchal  (1920) 

Mann  (1922) 

aurea  (L.)  Reichb 

5 

10 

Mann 

biennis  L..  . 

16 
20 
21 
20 

40 

Marchal  (1920) 

Rosenberg  (1918) 
Rosenberg  (1920) 
Mann  (1922) 

blattarioides  Vill... 

4 
4 

8 
8 

Marchal  (1920) 

Rosenberg  (1920) 
Mann 

breviflora  Delile 

4 

8 

Mann 

bidbosa  (L.)  Tausch 

9 

18 

Mann 

bursifolia  L.                     

4 

8 

Mann 

capillaris  (L.)  Wallr 

3 

6 

Rosenberg  (1909),  Mann  (1922) 

dioscoridis  L 

4 
4 

8 

Marchal  (1920) 

Mann  (1922) 

foetida  L 

4 
4 
5 

8 
10 

Marchal  (1920) 

Rosenberg  (1918) 
Mann  (1922) 

grandiflora  Tausch.          

4 

8 

Mann 

incarnata  Tausch 

4 

8 

Mann 

japonica  (L.)  Benth. 

8 

16 

Tahara  (1910),  Mann  (1922) 

myriocephala  Coss.  et  D.  R 

4 

8 

Mann  (1922) 

*  Marchal  gives  1914  as  the  date  of  his  counts,  but  they  were  not  published  until  1920. 
t  Figured  but  not  mentioned  in  the  text. 

J  Cited  from  Report  of  the  College  of  Agriculture,  University  of  California,  July  1,  1921-June  30 
1922. 


300  University  of  California  Publications  in  Agricultural  Sciences      [Vol. 

TABLE  1— (Continued) 


Number 

Species 

N 

2N 

Author 

neglecta  L 

4 

8 

Rosenberg  (1918),  Mann  (1922) 

palestina  Boiss.  Bornmuller 

4 

8 

Mann 

parviflora  Desf 

4 

8 

Rosenberg  (1918),  Mann  (1922) 

pulchra  L 

4 

8 

Rosenberg  (1920),  Mann  (1922) 

rubra  L 

4 
5 

10 

Marchal  (1920) 

Rosenberg  (1918),  Mann  (1922) 

setosa  Hall 

4 

8 

Mann  (1922) 

sibirica  L.... 

4 
5 

10 

Marchal  (1920) 

Mann  (1922) 

Sieberi  Boiss 

6 

12 

Mann  (1922) 

taraxacifolia  Thuill 

6 

4 

12 

8 

Beer  (1912) 

Digby  (1914),  Mann  (1922) 

tectorum  L.... 

4 

8 

Juel  (1905),  Mann  (1922) 

vesicaria  L 

4 

8 

Mann 

Table  1  shows  that,  while  four  is  the  most  common  haploid  number 
for  the  twenty  species  studied,  five  is  also  fairly  frequent.  The  other 
numbers  (3,  6,  8,  9,  and  20)  are  each  represented  by  a  single  species.  It 
is  obvious  that  chromosome  measurement  should  show  whether  cross- 
division,  union  into  multiples,  addition  by  non-disjunction,  or  combina- 
tions of  these  methods  are  sufficient  to  account  for  the  differences  in 
number  found  in  the  genus.  It  is  also  possible  that  hybridization 
between  species  with  different  chromosome  numbers  might  account  for 
the  origin  of  certain  cytological  peculiarities. 

For  some  species  the  cytological  material  is  far  more  abundant  than 
it  is  for  others,  so  that  it  is  possible  to  measure  only  somatic  metaphases 
in  which  all  the  chromosomes  are  fairly  straight.  The  tendency  of  the 
long  chromosomes  of  Crepis  to  twist  is  a  source  of  considerable  error 
where  relatively  poor  material  is  available.  The  finest  metaphase 
figures  are  to  be  found  in  the  upper  portion  of  the  rapidly  growing 
region  of  the  root  in  seedlings,  and  in  roots  from  adult  plants.  The 
region  containing  fine  figures  is  greater  in  roots  from  the  latter  than 


1925]     Mann:  Chromosome  Number  and  Individuality  in  lite  Genus  Crepis        301 

in  the  short  root  of  the  cotyledon  stage,  because  there  is  a  longer  growing 
area  in  which  the  cytoplasm  is  less  dense  than  it  is  at  the  tip,  so  that 
the  chromosomes  spread  out  more  freely  and  the  picture  is  less  obscured 
by  cytoplasmic  inclusions. 

Table  3  is  a  compilation  of  measurement  data  for  somatic  metaphase 
figures  in  nineteen  species  of  Crepis.  In  each  case,  except  japonica 
and  sieberi,  ten  somatic  polar  metaphases  were  drawn  with  a  camera 
lucida.  The  magnification  of  the  drawings  is  4000  diameters.  A 
moistened  thread  was  placed  along  the  center  of  the  drawing  of  each 
chromosome,  and  then  straightened  and  measured  in  millimeters.  The 
figures  were  then  placed  in  columns,  the  two  largest  in  the  first,  and  so 
on  down  to  the  two  smallest.  A  sample  of  these  records  for  a  five- 
pair  species,  alpina,  is  given  below  in  table  2. 


TABLE  2 

Actual  Measurements  of  Drawings 


Differences  from  Average 


1 

2 

3 

4 

5 

Total 
Length 

1 

2 

3 

4 

5 

32  mm 

25 

mm 

14  mm 

13.5mm 

13mm. 

31 

27 

14 

13 

12.5 

195  mm. 

+5.8 

+5.7 

-0.5 

+0.4 

+0.8 

22.5 

20 

15.5 

13 

11.5 

24.5 

18 

14.5 

13 

11 

163  mm. 

-1.7 

-1.3 

+  1.0 

-0.1 

-0.7 

30.5 

21 

17 

14.5 

12  5 

22 

19 

15 

14.5 

13 

179  mm. 

+4.3 

-0.3 

+2.5 

+  14 

+0.8 

21.5 

17 

13 

12 

10.5 

23.5 

19 

13 

12 

11.5 

153  mm. 

-2.7 

-2.3 

-1.5 

-1.1 

-0.7 

23 

21. 

5 

16.5 

14 

12 

29 

20 

15 

12 

11.5 

174  mm. 

+2.8 

+0.2 

+2.0 

+0.9 

-0.2 

It  is  evident  that  even  measurement  by  the  rather  crude  method 
described  above  gives  a  fairly  definite  clue  to  the  individuality  of  the 
species.  It  will  also  be  noted  that  when  the  larger  figure  of  each  set 
is  compared  with  the  average  for  the  chromosome,  obtained  by  dividing 
the  sum  of  the  ten  larger  of  the  twenty  chromosomes  of  one  type  by  ten, 
the  deviations  for  any  one  metaphase  set  are  generally  in  the  same 
direction  (+  or  — ).  (See  column  headed  "Differences  from  the 
average.")  This  deviation  indicates  that  the  error  of  measurement 
was  not  sufficient  to  conceal  the  fact  that  the  chromosome  lengths  of  a 
species  maintain  certain  size  relations  at  least  throughout  the  later 
periods  of  shortening.     It  also  shows  that  it  is  fair  to  use  an  average 


302 


University  of  California  Publications  in  Agricultural  Sciences      [Vol.  2 


so  obtained  in  a  comparative  study  like  this.  The  larger  figure  of 
each  set  was  considered  the  more  accurate  measurement  and  hence 
was  used  to  secure  the  'corrected'  totals  and  averages  which  appear  in 
table  3. 

TABLE  3 
Measurement  Data  for  Nineteen  Species  of  Crepis 


Species 


C.  capillaris 

C.  neglecta 

C.  setosa 

C.  parviflora 

C.  bursifolia 

C.  aurea 

C.  aspera 

C.  alpina 

C.  taraxacifolia 

C.  tectorum 

C.  blattarioides . . 

C.  japonica  a 

C.  foetida 

C.  bulbosa 

rubra 

dioscoridis 

sieberi  a 

pulchra 

sibirica 


Hap- 
loid 

chromo- 
some 

number 

Cor- 
rected 
average 

total 
length 

3 

61.4 

4 

61.7 

4 

63.2 

4 

69.9 

4 

78.5 

5 

83.5 

4 

82.6 

5 

87.3 

4 

88.4 

4 

88.7 

4 

91.1 

8 

92.6 

5 

93.7 

9 

100.5 

5 

102.9 

4 

109.4 

6 

109.6 

4 

112.1 

5 

143.6 

Corrected  average  for  individual  chromosomes 


26.2 

20.4 

14.8 

24.5 

16.2 

11.2 

9.8 

22.3 

17.8 

14.0 

9.1 

25.3 

20.5 

14.4 

9.7 

24.3 

22.0 

19.5 

12.7 

21.0 

18.0 

16.2 

15.1 

13.2 

23.9 

21.5 

19.7 

17.5 

26.2 

21.3 

14.5 

13  1 

12.2 

26.1 

23.3 

21.2 

17.8 

28.1 

23.2 

20.2 

17.2 

29.0 

23.8 

20.6 

17.7 

15.7 

13.5 

12.2 

11.5 

10.8 

10.0 

9.7 

9.2 

25.0 

20.8 

17.7 

15.8 

14.4 

13.9 

12.8 

12.1 

11  7 

11.1 

10.6 

10.1 

9.6 

29.4 

23.9 

18.5 

16.2 

14.9 

35.9 

29.3 

24.9 

19.3 

26.8 

21.4 

17.7 

16.0 

15.2 

12.5 

36.7 

30.6 

25.5 

19.3 

41.9 

32.4 

27.6 

23.2 

18.5 

8.6 


a  Averages  from  less  than  ten  figures. 

The  reliability  of  such  measurements  and  the  evidence  for  the 
constancy  of  specific  individuality  have  been  further  corroborated  by 
a  study  of  chromosome  measurements  of  the  Fi's  of  two  species-hybrids, 
setosa  X  tectorum  (fig.  1)  and  setosa  X  dioscoridis  (fig.  2).1  It  will  be 
noted  from  table  3  that  all  three  species  involved  have  four  pairs  and 
that  the  chromosome  sizes  are  far  more  different  in  the  two  latter  than 
in  the  two  former  species.  In  both  Fi's,  however,  it  was  possible  to 
determine  the  source  of  the  chromosomes  by  means  of  measurement 
data,  and  this  was  facilitated  by  the  peculiar  semidetached  tip  of  the 
longest  chromosome  of  setosa  (fig.  3),  by  which  it  may  usually  be  identi- 
fied. Since  only  one  member  of  a  set  is  present  in  each  Fi  figure,  it 
seemed  best  to  compare  the  averages  for  the  Fi's  with  the  uncorrected 
averages  for  the  species  involved.     The  results  are  tabulated  below: 

1  For  the  use  of  these  hybrids  and  the  data  on  hybridization  given  below,  I  am 
indebted  to  Dr.  J.  L.  Collins  of  this  laboratory. 


1925]     Mann:  Chromosome  Number  and  Individuality  in  the  Genus  Crepi-s        303 

TABLE  4 


setosa  X  dioscoridis 

39.9 

33.6 

28.9 

23 . 1 

22.1 
22.3 

18.1 

17.8 

13.7 
14.0 

10.3 

selosa 

9.1 

dioscoridis 

34.2 

28.9 

24.9 

20.6 

+5.7 

+4.7 

+4.0 

+2.5 

-0.2 

+0.3 

-0.3 

+  1.2 

selosa  X  teclorutn 

29.4 

24.1 

21.2 

16.8 

21.0 
22.3 

18.9 

17.8 

13.3 
14.0 

8.9 

setosa 

9.1 

lector  um 

28.1 

23.2 

20.2 

17.2 

+  13 

+0.9 

+  1.0 

-0.4 

-1.3 

+  11 

-0.7 

-0.2 

The  important  point  is  that  one  can  identify  the  chromosomes  of 
dioscoridis  and  of  tectorum  by  measurement  when  they  are  in  combina- 
tion with  those  of  setosa  in  an  Fi  hybrid,  so  that  it  is  evident  that  the 
specific  differences  in  length  noted  are  not  the  product  of  interaction 
between  a  certain  cytoplasm  and  its  chromosomes. 

Since  abundant  material  was  available  for  capillaris  (fig.  6),  the  first 
measurements,  which  were  made  on  ten  figures  about  as  good  as  the 
average  for  all  species,  were  checked  by  the  use,  first,  of  a  mixture  of 
slightly  different  metaphase  stages  (beginning  to  almost  complete  divi- 
sion) from  a  very  short  region  of  a  single  root  tip,  and,  second,  of  a 
mixture  from  undivided  figures  from  two  different  roots.  These 
measurements  show  that  averages  for  one  chromosome  in  three  different 
sets  of  ten  from  the  same  species  may  differ  by  as  much  as  3.55  mm., 
but  that  the  averages  give,  in  each  case,  very  nearly  the  same  differ- 
ences between  the  lengths  of  the  different  pairs. 


COMPARISON  OF  SPECIES 

Crepis  neglecta  (fig.  7)  has  a  very  characteristic  individuality,  two 
of  the  pairs  being  very  similar  and  distinctly  shorter  than  any  of  the 
chromosomes  of  capillaris.  Its  total  length  is  very  similar  to  that  of 
capillaris,  so  much  so  that  one  is  inclined  to  test  the  cross-division 
hypothesis  for  this  species.  If  the  two  shortest  averages  are  added, 
their  sum  is  practically  the  same  as  the  average  for  the  intermediate 
chromosome  of  capillaris  and  the  other  average  lengths  are  very  similar. 


capillaris. 
neglecta.... 


26.2 
24.5 


20.4 
11.2+9.8=21.0 


14.8 
16.2 


■1.7 


+0.6       +1.4 


Attempts  to  cross  the  two  species  have  as  yet  been  unsuccessful. 


304  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  2 

Setosa  (fig.  3),  like  neglecta,  differs  little  from  capillaris  in  total 
length.  It  contains,  however,  only  one  pair  of  chromosomes  shorter 
than  any  in  capillaris;  otherwise  it  is  rather  similar  to  it. 

capillaris 26.2         20.4         14.8 

setosa 22.3         17.8         14.0  9.1 

-3.9       -2.6       -0.8       +9.1 

It  has  already  been  noted  that  the  longest  chromosome  of  setosa  has 
a  semidetached  tip  by  which  it  may  be  recognized.  This  tip  is  usually 
at  an  angle  to  the  main  portion  of  the  chromosome.  In  the  figures 
given  above  the  longest  chromosome  of  setosa  appears  to  have  lost  a 
portion  of  its  length,  while  another  pair  of  chromosomes  averaging 
about  ten  units  has  been  added.  It  is  also  possible  that  the  longest 
chromosome  has  cross-divided,  and  that  the  peculiar  chromosome  of 
setosa  really  corresponds  to  the  intermediate  of  capillaris. 

capillaris 26.2        20.4         14.8 

setosa 17.8+9.1=26.9         22.3         14.0 

+0.7       +1.9       -0.8 

If  either  of  these  possibilities  represented  the  whole  truth  concerning 
the  difference  between  the  two  species,  we  should  expect  reduction  to 
be  fairly  normal  following  hybridization.  As  a  matter  of  fact,  no 
pairing  occurs  in  the  Fi  setosa  (N  =  4)  X  capillar is  (N  =  3)  (Collins  and 
Mann,  1923),  and  as  a  consequence  gametes  are  formed  with  3,  4,  and 
6  chromosomes  as  shown  by  five  plants  (backcrosses  to  setosa),  which 
have  7,  8,  and  10  somatic  chromosomes.  It  seems  possible  that  new 
types  differing  in  number  and  combination  of  chromosomes  may  be 
obtained  by  selfing  such  plants  as  the  backcrosses  with  ten  chromosomes. 

Crepis  parviflora  (fig.  8)  has  a  chromosome  individuality  much  like 
that  of  setosa;  the  longer  chromosome,  however,  averages  slightly  longer 
and  does  not  appear  to  have  a  semidetached  tip. 

setosa 22.3         17.8         14.0  9.0 

parviflora 25.3         20.5         14.4  9.7 

+3.0       +2.7       +0.4       +0.7 

It  is  evident  that  parviflora  is  more  similar  to  capillaris  than  setosa, 
but  like  setosa  it  has  an  additional  short  pair  of  chromosomes. 

capillaris 26.2        20.4         14.8 

parviflora 25.3         20.5         14.4  9.7 

-0.9       +0.1       -0.4       +9.7 

The  first  hypothesis  for  setosa  appears  to  be  the  more  probable  for 
parviflora.  If  it  were  true,  one  would  have  to  account  for  the  additional 
chromosome  of  9.7  units  by  hybridization  between  two  such  forms  as 


1925]     Ahum:  (.'hromtisnmc  X  umber  and  Individuality  in  the  Genus  Crepis        305 

neglecta  and  capillar  is.  The  hybridization  results  for  setosaX  capillar is 
given  above  indicate  that  new  types  with  new  combinations  of  chromo- 
somes may  arise  in  this  manner.  It  will  be  interesting  to  observe  the 
results  of  crossing  setosa  and  parviflora. 

Bur  si  folia  (fig.  9)  appears  to  have  an  extra  element  of  the  size  of  the 
intermediate  chromosome  of  the  capillaris  series: 

capillaris 26.2  20.4         14.8 

22  +  19.5 
bursifolia 24.3     =20.7         12.7 

-1.9  +0.3       -2.1 

It's  average  total  length  is  17.1  units  longer  than  that   of  capillaris. 
Crepis  taraxacifolia  (fig.  10),  tectorum  (fig.  5),  and  blattarioides  (fig. 
11)  have  very  similar  chromosome  groups. 

taraxacifolia 26.1         23.3         21.2         17.8 

blattarioides 29.0        23.8         20.6         17.7 

tectorum 28.1         23.2         20.2         17.2 

All  the  chromosomes  of  these  three  species  tend  to  average  slightly 
larger  than  those  of  capillaris,  but  the  differences  do  not  greatly  exceed 
those  of  the  different  averages  for  capillaris.  If  we  suppose  that  the 
intermediate  chromosome  of  capillaris  has  been  duplicated  in  this 
group  of  species,  the  correspondence  is  somewhat  bettered. 

Average  of  taraxacifolia,  tectorum,  and 

blattarioides 27.7  22.05  17.6 

Average  of  capillaris 26.2  20.40  14.8 

+  1.5  +1.65  +2.8 

It  is  obvious  that  the  relative  lengths  of  the  chromosomes  in  these 
three  species  are  very  similar  to  those  in  capillaris. 

Tectorum  and  capillaris  were  repeatedly  crossed  by  Collins  (1920), 
but  the  Fi  developed  only  as  far  as  the  cotyledon  stage.  This  indicates 
an  incompatibility  of  the  chromosomes  or  cytoplasm  hard  to  account 
for  on  the  basis  of  mere  addition  of  similar  material,  especially  when  one 
considers  that  trisomic  forms  which  come  to  maturity  appear  to  be  not 
uncommon  among  plants  and  animals.  It  will  be  very  interesting  to 
know  whether  others  of  the  group  of  species  indicated  above  will  behave 
like  tectorum  in  crosses  with  capillaris,  and  whether  they  will  intercross. 

Aspera  (fig.  12)  is  like  the  group  discussed  above  except  that  the 
longest  chromosome  appears  to  be  rather  short. 

capillaris 26.2  20.4         14.8 

21 .5  +  19.7 

aspera 23.9 =20.6         17.5 

-2.3  +0.2        +2.7 


306  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  2 

Crepis  bursifolia,  taraxacifolia,  tectorum,  blattarioides,  and  aspera 
might  all  be  derived  from  capillaris  by  duplication  of  the  intermediate 
pair  of  chromosomes. 

The  five-pair  species  listed  below,  although  generally  rather  similar 
in  chromosome  individuality,  show  certain  distinct  differences. 

Total 
length 

aurea 21.0       18.0       16.2       15  1       13  2       161.9 

alpina 26.2       21.3       14.5       13.1       12.2  174.6 

foetida 25.0      20.8       17.7       15.8       14.4  187.4 

rubra 29.4       23.9       18.5       16.2       14.9  205.8 

Aurea  (fig.  13)  is  outstanding  since  it  lacks  a  long  chromosome  of 
about  twenty-five  units.  The  figures  are  excellent,  so  that  the  averages 
must  be  considered  as  very  nearly  accurate.  Aurea  is  also  very  dis- 
tinctive morphologically.  Alpina  (fig.  14),  foetida  (fig.  15),  and  rubra 
(fig.  16)  are  much  more  alike  in  chromosome  individuality.  Alpina 
seems  to  have  three  pairs  resembling  the  shortest  chromosome  of 
capillaris,  and  to  be  cytologically  very  like  it  otherwise. 

capillaris 26.2         20.4  14.8 

14.5  +  13.1+12.2 
alpina 26.2         21.3         — ' =  13.2 

0  +0.9  -1.6 

Foetida  might  also  have  three  duplicates  of  the  shortest  chromosome 
of  capillaris. 

capillaris 26.2         20.4  14.8 

17.7  +  15.8+14.4 
foetida 25.0         20.8        ■ ! =  15.9 

-1.2       +0.4  +1.1 

The  figures  for  rubra  compare  better  with  those  of  capillaris  if  we  average 
the  two  intermediates  and  the  two  shortest  together. 

capillaris 26.2  20.4  14.8 

23.9  +  18.5  16.2  +  14.9 

rubra 29.4  -=21.2  -  =  15.5 

2 2 

+3.2  +0.8  +0.7 

It  was  noted  above  that  Rosenberg  (1918)  suggested  that  probably  the 
small  chromosome  of  capillaris  had  been  duplicated  twice  for  rubra. 
It  will  be  seen  from  the  figures  that  duplication  of  the  intermediate 
and  of  the  short  chromosome  appears  more  probable  on  the  basis  of 
the  measurements  presented  here. 


1925]     Mann:  Chromosome  Number  and  Individuality  in  the  Genus  Crepis        307 

Crepis  japonica  (N  =  8)  (fig.  17)  and  bulbosa  (N  =  9)  (fig.  18)  are 
rather  similar  in  chromosome  individuality,  but  are  totally  different 
from  all  the  rest  of  the  species  studied  in  chromosome  number  and  size. 

japonica 15.7     13.5     12.2     11.5     10.8     10.0      9.7     9.2 

bulbosa 13.9     12.8     12.1     11.7     11.1     10.6     10.1     9.6     8.6 

It  is,  of  course,  possible  that  japonica  might  have  been  derived  from  a 
species  like  tectorum  by  cross-division  of  every  chromosome,  or  vice 
versa.  When  we  test  this  hypothesis  by  adding  the  averages  for  the 
two  largest,  the  next  two,  etc.,  of  japonica  together,  the  results  are 

rather  striking. 

15.7  12.2  10.8  9.7 

japonica |           13.5  11.5  10.0  9.2 

i          29.2  23.7  20.8  18.9 

tectorum 28.1  23.2  20.2  17.2 

+  1.1  +0.5  +0.6  +1.7 

It  is  at  least  obvious  that  tetraploidy  could  not  explain  the  chromosome 
individuality  of  japonica  while  cross-division  might  do  so. 

Crepis  sieberi  (fig.  19)  is  the  only  species  so  far  studied  which  has 
six  pairs  of  chromosomes.  It  looks  as  if  it  might  have  four  pairs  of 
short  chromosomes: 

capillaris 26.2         20.4  14.8 

17.7  +  16  +  15.2  +  12.5 

sieberi 26.8         21.4 — =15.3 

4 

+0.6       +1.0  +0.5 

or  two  intermediate  and  three  short  pairs: 

capillaris...         26.2  20.4  14.8 

21.4  +  17.7  16  +  15.2  +  12.5 

sieberi 26.8         ! =19.5         ! ! =14.6 

2 3 

+0.6  -0.9  -0.2 

Crepis  pulchra  (fig.  21)  and  dioscoridis  (fig.  4)  are  very  similar  to 
one  another  in  chromosome  length. 

pulchra 36.7         30.6         25.5         19.3 

dioscoridis 35.9         29.3         24.9         19.3 

Difference 0.8  1.3  0.6  0 

C.  sibirica  (fig.  23),  with  five  pairs,  resembles  pulchra  and  dioscoridis 
in  choromosome  measurements,  and  the  average  length  of  the  two 
longest  chromosomes,  36.5,  indicates  that  it  may  have  two  instead  of 
one  of  the  longest  type  of  chromosome. 


308  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  '2 

41.9+32.4 

sibirica =37.1         27.6         23.2         18.5 

2 

dioscoridis 35.9         29.3         24.9         19.3 

Difference 1.2  1.7*         1.7  0.8 

If  we  suppose  that  this  group  of  species  has  been  derived  from  a 
type  like  capillaris,  we  must  consider  that  the  longest  chromosome 
represents  a  multiple.  If  we  subtract  the  intermediate  average  for 
capillaris  (20.4)  from  the  average  of  the  longest  chromosomes  of  all 
three  species  in  this  group  (36.3),  the  remainder,  15.9,  is  only  1.1  units 
longer  than  the  shortest  chromosome  of  capillaris,  indicating  that  an 
intermediate  and  a  short  chromosome  might  have  united  end  to  end 
to  form  an  element  averaging  36.3  units.  Then  if  we  average  the  two 
shortest  chromosomes  of  these  three  species  with  the  chromosome  of 
20.4  units,  which,  we  have  supposed  has  united  with  a  short  element, 
the  average,  19.9,  is  so  like  the  intermediate  of  capillaris  as  to  suggest 
that  it  may  have  been  duplicated  in  the  group  under  consideration. 
When  we  look  at  the  averages  now,  the  figures  compare  very  well. 

capillaris 26.2         20.4         14.8 

pulchra,  dioscoridis,  ,>0  c  i  oq  q_i_27  fi 

and  sibirica —=29.1         19.9        15.9 

3 

+2.9       -0.5       +1.1 

These  species  obviously  form  a  group  by  themselves,  especially 
since  it  has  been  shown  that  the  great  size  of  the  chromosomes  in 
dioscoridis  is  maintained  upon  hybridization  with  a  species  like  setosa. 


DISCUSSION 

For  two  reasons  it  is  impossible  to  make  any  sweeping  general- 
izations at  this  time  concerning  the  data  presented  here.  First,  we  do 
not  yet  know  how  species  differing  in  chromosome  number  can  arise, 
and  second,  we  know  too  little  about  the  genetics  of  Crepis.  There  are 
two  known  methods  by  which  a  single  pair  of  chromosomes  can  be  added 
to  a  complex,  non-disjunction  and  species-hybridization,  but  in  neither 
case  has  it  been  proved  that  stable  types  would  ever  result;  and  the 
formation  of  new  species  presupposes  stability.  It  has.  been  suggested 
that  it  is  very  improbable  that  stability  is  to  be  expected  of  tetrasomic 
individuals  because  the  complex  as  a  whole  is  unbalanced  by  the  addi- 
tion of  chromosomes.  This  view  seems  to  be  borne  out  by  observations 
on  the  cytology  of  tetrasomic  plants  of  Datura  (Belling  and  Blakeslee, 


1925]     Mann:  Chromosome  Number  and  Individuality  in  the  Genus  Crcpis         309 

1924)  and  Matthiola  (Frost  and  Mann,  1924).  Both  of  those  tetrasomic 
types  are  even  feebler  than  the  trisomic  plants,  and  hence  would  have 
little  chance  of  survival  under  unfavorable  environmental  conditions. 
The  possibilities  of  species-hybridization  as  a  source  of  differences 
in  chromosome  number  within  a  genus  are  still  less  known.  It  might 
be  argued  with  some  plausibility  that  if  a  tetrasomic  condition  is 
unbalancing  and  associated  with  lessened  viability,  even  less  in  the 
way  of  stability  and  viability  should  be  expected  of  organisms  having 
a  pair  of  chromosomes  from  another  species  added  to  a  complete  specific 
complex.  The  Drosophila  workers  have  found,  however  (Morgan, 
1922),  that  a  similar  genie  structure  characterizes  the  chromosomes  of 
several  species  of  that  genus,  and  if  this  is  true  of  Crepis,  one  method  may 
be  as  probable  as  the  other.  It  has  been  shown  (Collins  and  Mann, 
1923)  that  new  types  with  more  chromosomes  than  either  species 
possesses  are  formed  when  the  Fi  C.  setosaXC.  capillaris  is  backcrossed 
to  setosa.  It  is  only  through  further  work  on  such  types  that  the 
question  of  stability  can  be  answered.  The  theoretical  and  practical 
value  of  such  work  is  self-evident. 

While  the  little  work  that  has  so  far  been  done  on  tetrasomic  plants 
tends  to  show  that  they  would  be  expected  to  be  somewhat  unstable 
genetically,  tetraploid  plants,  e.  g.,  Oenothera  gigas,  breed  true.  That 
Crepis  biennis  may  be  an  octaploid  from  a  five-pair  species  is  indicated 
by  the  following  experimental  evidence : 

1.  In  the  Fi  C.  setosaXC.  biennis  the  twenty  pairs  of  chromosomes 
from  biennis  form  ten  pairs. 

2.  In  the  backcross  of  this  Fi  to  biennis  the  thirty  chromosomes 
from  C.  biennis  form  fifteen  pairs. 

The  great  size  and  vigor  which  distinguish  it  from  the  other  species 
studied  also  indicate  that  it  is  polyploid.  The  evidence  from  chromo- 
some measurements  indicates  strongly  that  Crepis  biennis  is  the  only 
one  of  the  twenty  species  discussed  in  this  paper  that  could  owe  its 
origin  to  polyploidy. 

It  would  seem  possible  that,  if  the  whole  complex  of  one  species  were 
added  to  that  of  another  by  segregation  following  species-hybridization, 
zygotes  formed  by  the  union  of  two  such  gametes  might  be  expected  to 
give  stable  races  differing  in  chromosome  number  from  other  species 
of  the  genus.  There  is  no  evidence  that  such  a  procedure  has  occurred 
in  any  of  the  species  of  Crepis  discussed  above. 

There  is  at  present  little  evidence  that  whole  chromosomes  can  be 
lost  and  the  resulting  organisms  be  expected  to  give  rise  to  new  species. 
Genet  ical  and  cytological  results  on  Drosophila  (Bridges,  1921)  indicate 


310  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  2 

that  while  53  per  cent  of  the  expected  flies  lacking  one  of  the  small 
fourth  chromosomes  live,  they  are  imperfect,  weak,  and  often  sterile. 
That  a  small  portion  of  a  chromosome  may  be  lost  or  inactivated  is 
indicated  also  by  work  on  this  fly  (Bridges,  1919).  Loss  of  this  strain 
is  attributed  to  the  injurious  effect  of  the  deficiency  upon  viability, 
fertility,  and  productivity. 

While  loss  of  chromosomes  appears  to  be  somewhat  improbable  as  a 
method  by  which  one  species  can  come  to  differ  from  another  in  chromo- 
some number,  the  chromosome  number  of  some  species  may  be  reduced 
as  a  result  of  permanent  end-to-end  union  of  certain  chromosomes  to 
form  multiples.  The  differences  in  number  noted  for  the  Acrididae 
(McClung,  1917)  appear  to  be  of  this  type.  One  species,  Hesperotettix 
viridis,  shows  considerable  variation  in  chromosome  union  in  different 
individuals,  indicating  that  it  may  be  in  the  process  of  producing  new 
types  of  chromosome  grouping.  It  is  also  decidedly  variable  morpho- 
logically. 

There  is  some  observational  evidence  that  species  differ  from  one 
another  in  chromosome  number  due  to  cross-division  of  all  chromosomes 
of  a  complex.  Marchal  (1920),  for  example,  reported  that  in  the  section 
Medium  of  Campanula  the  size  of  each  chromosome  of  pollen  mother 
cells  is  less  when  the  haploid  specific  number  is  thirty-four  than  when 
it  is  seventeen. 

It  is  difficult  to  understand  how  cross-division  or  union  of  chromo- 
somes to  form  multiples  could  cause  specific  differences.  In  fact,  a 
case  from  Drosophila  reported  by  Mrs.  Morgan  (1922)  indicates  that 
while  end-to-end  union  of  the  X-chromosomes  may  affect  genetic 
results  it  has  no  effect  upon  specific  characters.  It  seems  simpler  to 
suppose  that  such  changes  in  chromosome  complexes  are  the  result 
rather  than  the  cause  of  genetical  differences  between  individuals,  such 
as  have  been  noted  for  Hesperotettix  viridis  and  for  the  different  species 
of  the  Acrididae. 

In  the  genus  Drosophila,  it  has  been  shown  that  chromosomes  that 
look  alike  may  carry  very  different  genes.  For  example,  in  D.  willistoni, 
Metz  and  Lancefield  (1922)  report  that  the  X-chromosome  is  a  V- 
shaped  element  similar  to  the  second  and  third  autosomes  of  D.  melano- 
gaster.  Without  this  genetic  evidence  one  would  have  said  that  these 
two  species  had  the  same  type  of  chromosome  complex.  Such  evidence 
is  a  timely  warning  to  those  who  would  draw  hasty  conclusions  on  the 
basis  of  data  like  those  given  above  for  Crepis.  The  genetical  results 
from  Crepis  are  still  too  scanty  to  permit  of  such  tests. 


1925]     Maim:  Chromosome  Number  and  Individuality  in  the  Genus  Crepis        311 


SUMMARY  AND  CONCLUSIONS 

1.  With  the  exception  of  neglecta  and  possibly  setosa,  all  the  species 
of  Crepis  studied  show  significant  increases  in  total  length  of  the  chromo- 
some complex  over  that  of  capillaris,  the  single  species  with  three  pairs 
of  chromosomes. 

2.  Generally  speaking,  increased  number  is  associated  with 
increased  total  length,  but  there  are  certain  exceptions. 

3.  In  so  far  as  studies  on  chromosome  individuality  can  determine, 
five  of  the  species  with  four  pairs  of  chromosomes  might  have  two 
pairs  like  the  intermediate  chromosome  of  capillaris. 

4.  In  Crepis  neglecta  (N  =  4)  the  two  shortest  chromosomes  might 
have  been  derived  by  cross-division  of  a  chromosome  of  the  length  of 
the  intermediate  chromosome  of  capillaris. 

5.  Crepis  setosa  (N  =  4)  and  parvi flora  (N  =  4)  are  very  similar  in 
total  length  and  quite  unlike  all  of  the  other  species. 

6.  Crepis  dioscoridis  (N  =  4)  and  pulchra  (N  =  4)  have  a  long  pair 
of  chromosomes  which  is  not  represented  in  capillaris  or  in  the  other 
four  chromosome  species.  It  is  possible  that  it  might  be  a  multiple 
chromosome.  That  this  difference  in  length  is  not  due  to  a  difference 
in  physiological  condition  or  to  error  is  shown  by  the  fact  that  it  is 
maintained  when  the  dioscoridis  chromosomes  are  in  setosa  cytoplasm 
in  an  Fi  between  these  two  species.  All  the  chromosomes  of  these  two 
species  can  be  distinguished  in  this  Fx. 

7.  Aurea  stands  out  among  the  species  with  five  pairs  because  of 
its  lack  of  an  element  like  the  longest  chromosome  of  capillaris.  The 
complexes  of  rubra,  foetida,  and  alpina  might  all  have  been  derived  by 
duplication  of  certain  chromosomes  of  capillaris.  Sibirica  seems  to 
possess  two  chromosomes  like  the  large  element  of  dioscoridis  and 
pulchra. 

8.  The  single  species  with  six  pairs,  sieberi,  has  chromosomes  which 
are  enough  like  those  of  capillaris  in  length  to  have  been  derived  from 
it  by  chromosomal  duplication.  There  appear  to  be  but  one  pair 
of  the  large  and  the  intermediate  types,  and  four  pairs  like  the  short 
chromosomes. 

9.  Japonica  with  eight  pairs  might  be  derived  by  cross-division  of 
all  chromosomes  of  a  species  like  tectorum. 

10.  Bulbosa  (N  =  9)  has  short  chromosomes  like  those  of  japonica. 


312  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  2 

11.  Biennis  (N  =  20)  has  chromosomes  comparable  in  size  to  those 
of  capillaris,  and  there  is  some  experimental  evidence  which  indicates 
that  it  is  a  polyploid  from  a  five-pair  species. 

12.  It  is  well  understood  that  these  data  are  simply  suggestive, 
but  it  is  hoped  that  they  may  be  of  some  use  in  taxonomic  and  hybridiza- 
tion studies  on  Crepis.  The  evidence,  based  on  especially  favorable 
cytological  material,  shows  that  it  is  entirely  unsafe  to  assume  that 
even  closely  related  species  which  have  the  same  chromosome  numbers 
are  identical  in  chromosome  individuality;  or  to  assume  polyploidy 
unless  the  sizes  of  the  chromosomes  have  been  compared. 


LITERATURE  CITED 

Beer,  R. 

1912.     Studios  in  spore  development.     II.   On  structure  and  division  of  the 
nuclei  in  the  Compositac.     Ann.  Bot.,  vol.  26,  pp.  705-726. 
Belling,  J. 

1922.  The  cytology  of  Datura  mutants.     Carnegie  Institute  Year  Book,  vol. 

21,  pp.  99-100. 
Belling,  J.,  and  Blakeslee,  A.  F. 

1924.     The  distribution  of  chromosomes  in  tetraploid  Daturas.     Am.  Nat.,  vol. 
58,  pp..  60-70. 
Bridges,  C.  B. 

1919.  Vermilion-deficiency.     Jour.  Genera]  Physiology,  vol.  1,  pp.  645-656. 

1921.  Genctical  and  cytological  proof  of  non-disjunction  of  the  fourth  chromo- 
some of  Drosophila  melanogaster.  Proc.  Nat.  Acad.  Sci.,  vol.  7,  pp. 
186-192. 

Collins,  J.  L.,  and  Mann,  M.  C. 

1923.  Interspecific  hybrids  in  Crepis.     II.  A  preliminary  report  on  the  results 

of  hybridizing  Crepis  setosa  Hall  with  C.  capillaris  (L.)  Wallr.  and 
with  C.  biennis  L.     Genetics,  vol.  8,  pp.  212-232. 

Digby,  L. 

1914.  Critical  study  of  the  cytology  of  Crepis  virens.  Arch.  f.  Zellforsch., 
vol.  12,  pp.  97-146. 

Frost,  H.  B.,  and  Mann,  M.  C. 

1924.  Mutant  forms  of  Matthiola  resulting  from  non-disjunction.     Am.  Nat., 

vol.  58,  pp.  569-572. 

JUEL,  H.  O. 

1905.     Die  Tetradenteilungen  bei  Taraxacum  und  anderen  Cichorieen.     Kungl. 
Svensk.  Vetensk.  Akad.,  Handl.,  vol.  39,  no.  4. 
McClung,  C.  E. 

1917.     The  multiple  chromosomes  of  Hesperotettix  and  Mermiria  (Orthoptera). 
Jour.  Morph.,  vol.  29,  pp.  519-590. 
Marchal,  E. 

1920.  Recherches  sur  les  variations  numeriques  des  chromosomes  dans  la  serie 

vegetale.     Memoires  de  l'Acadcmie  royale  de  Belgique,  ser.  2,  vol.  4, 
pp.  1-108. 


1925]     Mann:  Chromosome  Number  and  Individuality  in  the  Genus  Crepis         313 

Metz,  C.  W.,  and  Lancefield,  R. 

1922.     The  sex-linked  group  of  mutant  characters  in  Drosophila  willistoni.     Am. 
Nat.,  vol.  56,  pp.  211-241. 
Morgan,  L.  V. 

1922.     Non-criss-cross  inheritance  in  Drosophila  mclanogaster.     Biol.  Bull.,  vol. 
42,  pp.  267-274. 
Morgan,  T.  H. 

1922.     Croonian  lecture  on  the  mechanism  of  heredity.     Proc.  Roy.  Soc,  Sec. 
B,  vol.  94,  pp.  162-197. 
Rosenberg,  O. 

1909.  Zur  Kenntniss    von    den    Tetradenteilungen  der  Compositen.     Svensk. 

Bot.  Tidskr.,  vol.  3,  pp.  64-77. 
1918.     Chromosomenzahlen    und    Chromosomendimensionen    in    der    Gattung 

Crepis.     Arch.  f.  Bot.,  vol.  15,  pp.  1-16. 
1920.     Weitere  Untersuchungen  liber  die  Chromosomenverhaltnisse  in  Crepis. 

Svensk.  Bot,  Tidskr.,  vol.  14,  pp.  319-326. 
Tahara,  M. 

1910.  tlber    die    Zahl    der   Chromosomen    von    Crepis  japonica.     Bot.  Mag., 

Tokyo,  vol.  24. 


PLATE  53 


Somatic  metaphases  of  Crepis  species  magnified  4000  diameters,  using  a  B.  and 
L.  camera  lucida  mirror  at  50,  bar  at  110,  and  a  1.8  mm.  oil  objective  with  an  18X 
Zeiss  compensating  ocular.     Reduced  in  reproduction  to  1800  diameters. 

F\  setosaXtectorum 

Fi  setosaXdioscoridis 

setosa 

dioscoridis 

tectorum 


1. 
2. 
3. 
4. 

5. 
6. 

7. 


9. 
10. 
11. 
12. 


capillaris 

neglecta 

parviflora 

bursifolia 

taraxadfolia 

blattorioides 

aspera 


13. 

aurea 

14. 

alpina 

15. 

foetida 

16. 

rubra 

17. 

japonica 

18. 

bulbosa 

19. 

sieberi 

20. 

arrvplexifolia 

21. 

pulchra 

22. 

grandifolia 

23. 

sibirica 

24. 

biennis 

[314] 


UNIV.    CALIF.    PUBL.   AGRI.    SCI.    VOL.    2 


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UNIVERSITY    OF    CALIFORNIA    PUBLICATIONS 

IN 

AGRICULTURAL    SCIENCES 

Vol.  2,  No.  11,  pp.  315-341,  7  figures  in  text  March  6,  1926 


CHROMOSOME  NUMBER  AND  INDIVIDUALITY 

IN  THE  GENUS  CREPIS 
II.  THE  CHROMOSOMES  AND  TAXONOMIC  RELATIONSHIPS 

BY 

ERNEST  BROWN  BABCOCK  and  MARGARET  MANN  LESLEY 


CONTENTS 

PAGE 

Introduction 315 

Material  and  methods 316 

Acknowledgments 316 

Taxonomy  and  cytology  of  twenty-one  species  of  Crepis 317 

Literature  and  discussion 332 

Summary  and  conclusions 338 

Literature  cited 339 


INTRODUCTION 

For  the  past  three  years  we  have  been  accumulating  data  on  the 
taxonomy  and  cytology  of  the  genus  Crepis.  The  present  paper  repre- 
sents only  two  phases  of  our  general  project,  which  also  includes  exten- 
sive genetic  research  on  species  and  species  hybrids,  the  whole  under- 
taking being  an  effort  to  establish  a  natural  classification  of  a  genus 
which  has  been  a  source  of  considerable  difficulty  to  taxonomists  and 
which  presents  a  wide  array  of  chromosome  numbers.  In  addition  to 
number  we  have  examined  the  size  of  the  chromosomes  in  the  species 
studied,  in  the  hope  that  this  might  also  prove  useful  as  a  criterion 
in  classification. 

We  are  confining  our  discussion  to  species  which  we  have  been  able 
to  cultivate  in  the  greenhouse  or  garden  and  to  identify  with  certainty, 
a  procedure  which  has  thrown  considerable  light  on  the  classification. 
Ideally  the  taxonomist  should  know  his  species  as  they  appear  under 
natural  conditions,  but  obviously  this  is  impossible  for  any  one  botanist 
in  the  case  of  such  a  large  and  widely  distributed  genus  as  Crepis. 


316  University  of  California  Publications  in  Agricultural  Sciences      [Vol.2 

But,  even  though  field  studies  of  most  of  the  species  could  not  be  made, 
it  was  yet  necessary  to  cultivate  them  in  order  to  study  them  eyto- 
logically,  and  hence  it  has  been  possible  to  supplement  the  examination 
of  herbarium  material  by  observations  on  cultivated  plants  which  were 
grown  under  fairly  uniform  conditions.  By  this  method  it  has  been 
possible  to  show  that  certain  characters  (for  example,  nodding  position 
of  the  young  flower  heads)  which  have  been  used  by  some  authors  to 
separate  sections  of  the  genus,  are  variable  within  a  single  species. 

Crepis  was  chosen  in  the  first  place  because  certain  species  have 
small  chromosome  numbers  and  because  the  chromosomes  are  compara- 
tively easy  to  study  in  some  detail.  A  previous  paper  on  chromosome 
size  and  number  in  the  genus  (Mann.  1925)  contained  a  majority  of 
the  chromosome  data  herein  considered,  together  with  a  suggestion  as 
to  how  a  cytologist  would  be  tempted  to  group  the  species  studied.  In 
this  paper  we  have  added  somewhat  to  the  cytological  data  and  have 
attempted  to  utilize  both  the  cytological  and  the  taxonomieal  modes  of 
attack.  Generally  speaking,  this  method  has  proved  of  the  greatest 
usefulness;  and.  while  certain  irreconcilable  situations  still  appear  to 
exist,  we  have  reason  to  hope  that  future  developments — as  we  obtain 
more  species  and  make  further  studies — may  show  how  such  situations 
have  arisen  and  lead  the  way  to  a  (dearer  understanding  of  the  genus. 

MATERIAL  AND  METHODS 

The  species  of  Crepis  upon  winch  this  study  is  based  are  all  from 
the  Old  World,  and  have  mostly  been  obtained  through  the  cooperation 
of  European  botanists.  Since  we  desire  to  make  our  study  as  complete 
as  possible,  we  shall  greatly  appreciate  any  assistance  towards  obtain- 
ing viable  s Is  in-  roots  of  additional  species.     The  taxonomic  studies 

have  included  the  examination  of  both  dried  and  living  specimens,  and 
much  care  has  been  exercised  in  the  determination  of  all  this  material. 
The  cytological  methods  were  described  in  Mann  (1925). 

Acknowledgments 

The  investigations  herein  reported  were  conducted  in  part  through 
an  allotment  from  the  Adams  Fund.  It  is  with  pleasure  that  we 
acknowledge  the  assistance  of  Dr.  J.  L.  Collins  and  Mr.  C.  W.  Haney 
in  the  growing  of  cultures  and  in  providing  us  with  certain  data  on 
species  hybridization.  All  the  drawings  were  made  by  Helen  E. 
Rearwin,  whose  attention  to  accuracy  of  detail  is  gladly  acknowledged. 
Our  thanks  are  also  due  to  the  curators  of  herbaria  and  directors  of 


1926]         Bdbeoek— Lesley :  Chromosomes  and  Taxonomic  "Relationships  317 

botanic  gardens  in  numerous  institutions.  Many  taxonomic  and  other 
treatises  on  the  Compositae  have  been  consulted,  which  cannot  be  cited 
in  this  brief  paper. 

TAXONOMY    AND    CYTOLOGY   OF    TWENTY-ONE    SPECIES 

OF  CREPTS 

In  the  present  paper  we  do  not  wish  to  discuss  the  taxonomy  of 
Crepis  in  detail  or  to  propose  any  taxonomic  revision  of  the  genus,  but 
merely  to  set  forth  the  general  features  of  the  group  and  its  sub- 
divisions in  such  a  way  as  to  enable  the  reader  to  appreciate  some  of 
the  difficulties  involved  in  attempting  to  classify  the  species  according 
to  a  natural  system.  Also,  it  is  hoped  that  the  significance  of  the  cyto- 
logical  data  herein  presented  will  be  clearer  after  a  preliminary  con- 
sideration of  the  outstanding  morphological  resemblances  and  differ- 
ences to  be  found  within  this  group  of  plants. 

No  thoroughgoing  investigation  of  the  entire  genus  has  been  made.. 
Some  of  the  species  have  been  studied  since  the  time  of  Linnaeus  or 
even  earlier,  and  at  least  forty-four  other  generic  names  have  been 
applied  by  twenty-four  authors  in  attempting  to  classify  various  por- 
tions of  the  assemblage.  The  purposes  of  the  present  paper  can  be 
best  served  by  a  discussion  of  the  treatment  of  the  genus  given  by 
Hoffmann  in  Engler  and  Prantl's  Pflanzenfamilien.  This  treatment, 
represented  in  condensed  form  below,  includes  all  but  six  of  the  twenty- 
one  species  for  which  complete  data  as  to  chromosome  size  are  avail- 
able and  one  other  (C.  patula)  which  Ave  have  not  yet  been  able  to 
secure.  The  six  species  referred  to — blattarioides  Vill.,  bursifolia  L., 
neglecta  L.,  parviflora  Desf.,  montana  d'Urville,  and  setosa  Hall.  f. — 
are  all  easily  placed  in  Hoffmann's  categories  with  the  exception  of 
neglecta,  which  is  referred  to  Eucrepis  in  most  recent  floras  (see  p. 
327).  A  translation  of  Hoffmann's  description  of  the  genus  is  given 
below  "for  the  information  of  readers  who  are  not  familiar  with  this 
groups  of  plants.  His  analysis  of  the  genus  and  key  to  the  sections 
appear  in  table  1. 

Crepis  L. — Heads  small  to  rather  large,  yellow-  or  seldom  recb 
flowered,  borne  singly  or  in  panicles  of  variable  form ;  involucre  cylin- 
drical or  bell-shaped,  often  with  loose  or  appressed  outer  calyx,  the 
inner  fructiferous  bracts  often  becoming  stouter  and  harder  through- 
out or  along  the  middle  nerve ;  receptacle  naked  or  ciliate ;  fruit  10-30 
ribbed,  with  a  short  callosity  on  the  base,  reduced  or  beaked  at  the 
apex,  the  outer  fruits  sometimes  shaped  differently  from  the  inner 
ones ;  pappus  in  most  species  composed  of  soft  pliable  hairs,  seldom 
somewhat  brittle  and  brownish,  in  the  marginal  fruits  sometimes  lack- 
ing.— Herbs,  very  seldom  half-shrubby  plants.  Perhaps  170  species 
mostly  from  the  northern  hemisphere. 


318  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  2 


a  a- 

Fig.  1.    Achenes  of  Crepis  alpina — a,  marginal;  a',  inner.     X  7  circa. 


L'JiliiJ         Bab  cock-Lei  It  y :  Chromosomes  and  Taxonomic  "Relationships  319 


Fig.  2.     Marginal  and  inner  achenes  of:  b,  b',  Crepis  rubra;  c,  <•',  C.  foetidu. 

X  7  circa. 


320  University  of  California  Publications   in   Agricultural  Sciences      [Vol.  2 


TABLE   1 

Hoffmann  's  Key  to  the  Sections  of  Crepis  with  the  Addition  of  Six  Species 
Not  Listed  by  Him  and  References  to  Original  Drawings  of  Achenes 

A.  Pappus  bristles  very  short,  unequal,  the  longest  scarcely  as  long  as  the  width 

of  the  fruit,  very  readily  deciduous;  fruit  short-beaked. 

Sec.  I.  Ceramiocephalum  Schultz  Bip.* 
C.  patula  Poir. 

B.  Pappus  bristles  longer. 

(a)  Inner  or  all  the  fruits  long-beaked. 

Sec.  II.  Barkhausia  Much.* 

Fruits  all  beaked  (outer  sometimes  shorter  than  inner),  involucre 
mostly  with  outer  calyx,  seldom  imbricate.     Fig.  1,  a,  a' ;  Fig.  3,  d, 
e,  e'  g,  g'. 
C.  alpina  L.,  turaxaci folia  Thuill.,  bursifolia  L.,  setosa  Hall.  f. 
Sec.  III.  Anisoderis  Cass.* 

Outer  fruits  short-,  inner  long-beaked.     Fig.  2,  b,  b',  c.  <■'. 
C.  foetida  L.,  rubra  L. 
Sec.  IV.  Nemauchenes  Cass*   (in  part). 

Marginal    fruits   not    or    scarcely    beaked,    enclosed    within    the 
much   hardened    involucral   bracts;    ribs   prominent,   the   innermost 
enlarged    wing-like    so    the    fruits    seem    to    be    compressed;    inner 
fruits  prismatic  long-beaked.     Fig.  3,  h,  h' . 
C.  aspera  L. 

(b)  Fruits  reduced  at  the  apex,  but  not  beaked  or  only  short-beaked. 

Sec.  V.  Nemauchenes  Cass.*    (in   part). 

Except  for  the   scarcely   beaked  inner   fruits,   like  TV.      Fig.  4, 
k,  I'. 
C.  Dioscoridis  L. 
Sec.  VI.  Cymboseris  Boiss.* 

Marginal  fruits  compressed,  3-angled,  the  edges  winged,  enclosed 
by   the   inner   much   hardened  involucral    bracts,   without    pappus. 
Fig.  4,  m,  m' ,  m". 
C.  palaestina  Boiss.   (Boriim.). 
Sec.  VII.  Phaecasium  Cass.* 

Fruits  alike   in   shape  with  readily  deciduous   pappus   which  is 
mostly  absent  in  the  marginal  fruits,  inner  fructiferous  involucral 
bracts  much  hardened.     Fig.  4,  ft,  ft',  n". 
C.  pulchra  L. 
Sec.  VIII.  Aetheorrhiza  Cass.* 

Distinct  from  others   by   tuberous  root-stock,   fruits  all  similar 
in  shape.     Fig.  6,  «. 
C.  bulbosa  (L)  Tausch. 

Sec.  IX.  Eucrepis  DC. 

Roots   not   tuberous    (fusiform   or   root-stock    as    though   bitten 

off);  fruits  all  alike;  involucre  with  outer  calyx;  inner  fructiferous 

involucral  bracts  mostly  moderately  thickened.  Fig.  5,  o,  p,  q,  r,  s,  t. 

C.    capillaris    (L)    Wallr.,    neglecta    L.,    parviflora   Desf.,    tcctorum    L., 

biennis  L.,  montana  d'Urv. 

*  Described  as  a  genus. 


1  *  * — *  >  J  Babcock-Lesley:  Chromosomes  and  Taxonomic  Relationships  321 

Sec.  X.  Youngia  Cass.* 

Distinct  from  preceding  section  in  the  small  few-flowered  (8-15) 
heads.     Stem   few-leaved;   involucre  in  mature  fertile  heads  little 
changed.     Pappus  readily  deciduous.     Fig.  6,  v,  v'. 
C.  japonica  (L)  Benth. 

Sec.  XI.  Catonia  Much.* 

Involucre    imbricate,    often    black    hairy;    outer   bracts    shorter 
but  at  least  half  as  long  as  inner  bracts  and  forming  no  distinct 
outer  calyx,  in  mature  fertile  heads  flat  and  unchanged.     Fig.  6, 
w,  x,;  fig.  7,  y. 
C.  sibirica  L.,  aurea  (L)  Cass.,  blattarioides  Vill. 

We  shall  first  discuss  Hoffmann's  grouping  of  the  twenty-one 
species  now  before  us,  and  then  suggest  a  more  natural  grouping,  in 
order  that  the  cytologic  data  to  be  presented  may  be  more  intelligently 
considered.  It  will  be  noted  that  the  genus,  as  treated  by  Hoffmann, 
is  divided  into  three  subgenera  but  without  designating  them  as  such. 
The  first  consists  of  the  monotypie  section,  Ceramiocephalum ;  the 
second  (a)  contains  three  sections  all  characterized  by  having  fruits 
with  definite  beaks;  and  the  third  (?>),  comprising  the  remaining 
seven  sections,  contains  species  none  of  which  have  manifestly  beaked 
fruits.  It  was  long  ago  pointed  out  (Bischoff,  1851)  that  all  degrees 
of  development  of  the  beak  are  found  in  group  (a),  while  some  of  the 
species  included  in  group  (b)  have  fruits  with  very  short  or  obscurely 
developed  beaks.  But  this  seems  to  be  generally  looked  upon  as 
merely  part  of  the  evidence  of  relationship  within  the  whole  group 
and  as  part  of  the  argument  for  treating  it  as  a  single  genus. 

Section  I  is  set  apart  from  all  the  other  species,  probably  justifiably. 
but,  as  we  have  not  yet  been  able  to  work  with  living  material  of  this 
interesting  species,  it  is  unnecessary  to  give  it  further  consideration 
at  present. 

Subgenus  (a),  on  the  basis  of  fruit  characters  alone,  would  be 
better  rearranged  as  follows: 

Sec.  II.  Fruits  large,  the  inner  ones  10-18  mm.  long. 

C.  alpina,  foetida  rubra  (cf.  figs.  1  and  2). 
Sec.  III.  Fruits  small,  all  alike,  the  inner  ones  5-8  mm.  long. 

C.  bursifolia,  setosa,  taraxacifolia  (cf.  fig.  3,  d,  e,  g). 
Sec.  IV.  Fruits  small,  of  two  shapes,  marginal  ones  winged. 

C.  aspera  (cf.  fig.  3,  h,  h'). 

Furthermore,  the  above  rearrangement  is  not  inconsistent  with 
other  morphological  characters  of  diagnostic  value.  This  is  especially 
interesting  in  connection  with  the  cytological   evidence,   the  species 


*  Described  as  a  genus. 


322 


University  of  California  Publications  in  Agricultural  Sciences      [Vol.  2 


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324  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  2 

grouped  under  Section  II  all  having  5  pairs  of  chromosomes  of  similar 
size,  while  those  under  Sections  III  and  IV  have  4  pairs  but  differ 
somewhat  in  individuality.  It  is  worthy  of  note  that  one  character 
commonly  used  in  distinguishing  between  these  species,  viz..  the  posi- 
tion assumed  by  the  young  flower  heads  before  anthesis.  whether  erect 
or  nodding,  has  been  found  to  be  too  variable  in  the  case  of  foetida  to 
make  it  of  diagnostic  value. 

In  its  dimorphous  fruits,  the  inner  ones  beaked  and  the  outer  ones 
winged,  C.  aspire  exhibits  relationship  with  Barkhausia  on  one  side 
and  the  Diascoridis  group  on  the  other  (cf.  fig.  4.  1c,  A').  Its  chromo- 
some group  resembles  those  of  the  three  Barkhausia  species  in  having 
chromosomes  of  medium  size,  and  it  has  been  crossed  with  two  of  these 
species.  But  these  hybrids  exhibit  very  abnormal  reduction  phe- 
nomena, whereas  hybrids  between  certain  Barkhausia  species  (vesi- 
caria,  MarscJxdlii  and  taraxacifolia)  show  normal  pairing  and  reduc- 
tion. Thus  all  the  evidence  indicates  that  aspera  belongs  in  a  class  by 
itself.  Furthermore,  ampleocifolia,  which  closely  resembles  aspera 
morphologically,  also  has  4  pairs  of  medium-sized  chromosomes 
(p.  331). 

Subgenus  (b)  is  a  heterogeneous  group  which  is  scarcely  capable 
of  satisfactory  classification  on  the  basis  of  fnih  characters  alone. 
Thus  in  the  case  of  sections  V,  VI,  and  V 1 1  there  is  much  stronger 
affinity,  as  indicated  by  comparative  morphology,  than  would  appear 
from  Hoffmann's  synopsis.  In  all  three  of  the  species  concerned  the 
inner  involucral  bracts  of  fructiferous  heads  are  conspicuously  thick- 
ened or  much  hardened.  Then,  too,  palaestina  has  a  combination  of 
some  of  the  distinguishing  characters  of  the  other  two  species,  and 
yet  it  is  in  no  sense  an  intermediate  form  such  as  mighl  arise  from 
hybridization.  The  flower  heads  in  palaestina  are  large  and  showy. 
and  the  marginal  fruits  are  enclosed  within  the  inner  involucral  bracts, 
in  these  respects  resembling  Diascoridis,  while  the  inner  fruits  bear  a 
strong  resemblance  to  those  of  pulchra.  Furthermore,  the  fruits  in 
pulchra,  contrary  to  Hoffmann,  are  sometimes  of  two  distinct  shapes, 
the  marginal  ones  being  flattened  as  in  palaestina  (  cf.  tig.  4).  Without 
going  into  further  details  at  this  time,  we  may  suggest  that  these  three 
sections  might  Avell  be  combined  into  one.  The  chromosome  groups 
of  pulchra  (N  =  4),  palaestina  (N  =  4),  and  Diascoridis  (N  =  4) 
are  indistinguishable,  and  the  F1  of  pulchra  X  palaestina  is  highly 
fertile. 

Section  VIII,  Aetheorrhiza,  must  stand  alone,  at  least  for  the 
present.     While  the  inflorescence  of  bulbosa  suggests  strong  relation- 


1920]  Bab  cock-Lesley:  Chromosome*  and  Taxonomic  Eelationships 


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326 


University  of  California  Publications  in  Agricultural  Sciences      [Vol.2 


ship  with  a  urea,  this  species  is  cytologically  very  different  from  all 
other  species  of  Crepis,  having  9  pairs  of  short  chromosomes.  The  only 
species  studied  which  it  at  all  resembles  in  tins  respect  is  japonica. 
which  has  8  pairs  of  chromosomes  of  similar  size. 


Fig.  6.     Typical  achen.es  of:  u,  Crepis  bulbosa;  v,  C.  japonica — v',  cross-section 
outline;  w,  C,  anna;  x,  ('.  blattarioides.     X  6.5  circa. 

Section  IX.  Eucrepis,  contains  six  of  our  twenty-one  species,  and 
on  the  basis  of  fruit  characters  alone  (cf.  fig.  5)  they  comprise  three 
groups,  as  follows:  1.  capillaris  and  parviflora;  2.  neglecta,  tectorum, 
montana;  3.  biennis,  lint  if  we  consider  habital  and  other  morpho- 
logical characters,  they  may  be  rearranged  as  follows:  1.  capillaris, 
parviflora,  neglecta;  2.  tectorum;  3.  biennis;  4.  aiontana.  Such  an 
arrangement  is  of  interest  when  considered  in  relation  to  the  chromo- 
somes of  these  species.  It  was  noted  (Mann,  1925)  that  the  total 
length  of  the  chromosome  group  in  capillaris  (N  =  3)  is  practically 
the  same  as  that  of  neglecta  (N  =  4),  while  parviflora  (N  =  4)  appears 
to  have  a  short  chromosome  added  to  a  complex  like  that  of  capillaris. 
The  chromosome  group  of  tectorum  (N=4)  could  not  be  differentiated 


19261 


Bdbcock— Lesley :  Chromosome*  and  Taxonomic  Relationships 


327 


-V 


Fig.  7.     Typical  achene  of:  y,  Crepis  sibhica.     X  7  circa. 

from  that  of  taraxacif  olia  in  Barkhausia,  but  biennis  (N  =  20)  and 
montana  (N  =  6)  stand  apart  from  all  other  species  from  the  stand- 
point of  chromosome  number. 

It  should  be  observed  that  C.  neglecta  has  long  been  a  troublesome 
species  to  students  of  this  difficult  genus.  In  the  Genera  Plantarum 
(Bentham  and  Hooker,  1873)  neglecta  is  considered  as  intermediate 


328  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  2 

between  Eucrepis  and  Lagoseries  (Barkhausia) ;  parviflora  was  given 
similar  intermediate  status,  but  this  is  manifestly  an  error.  In  the 
Flora  Orientalis  (Boissier,  1875)  we  find  a  statement  which  we  trans- 
late as  follows:  "As  the  achenes  gradually  diminish  into  a  short  beak, 
it  is  doubtful  whether  this  species  belongs  in  Eucrepis  or  Barkhausia; 
it  affords  a  connecting  link  between  the  two  sections."  Boissier  places 
it  under  Barkhausia,  presumably  because  the  young  flower  heads 
assume  a  nodding  position.  The  unreliability  of  this  character  has 
been  pointed  out.  Moreover,  recent  taxonomists  (e.g.,  Fiori,  1904) 
have  placed  neglect  a  in  Eucrepis,  where  it  seems  to  belong  rather  than 
in  Barkhausia,  as  its  fruits  are  variable  in  shape  and  even  when  they 
are  beaked  the  beak  is  very  short,  as  shown  in  figure  5g. 

Section  X,  Youngia,  is  represented  here  by  only  one  species,  but 
contains  several  others,  of  which  one  is  fuscipappa  (p.  331).  These 
comprise  a  very  distinct  group  in  certain  morphological  characters, 
insomuch  that  some  authors  have  suggested  placing  it  in  Lactuca. 
But  it  is  claimed  (Bentham  and  Hooker,  1873;  Hooker,  1882)  that  the 
species  of  this  group  (except  two  referred  to  Lactuca  or  Ixeris) 
resemble  Eucrepis  more  closely  than  Lactuca,  and  that  japonica,  which 
is  the  type  species  of  Cassini's  genus,  Youngia,  does  not  differ  much  in 
floral  characters  from  C.  parviflora,  a  statement  which  is  partially 
true,  although  a  number  of  differences  do  exist.  Tt  was  noted  above 
that  japonica  (N  =  8)  resembles  bulbosa  in  having  very  short  chromo- 
somes. It  is  the  only  species  knuwn  in  the  genus  with  8  small  chromo- 
somes (japonica  chromosomes  total  about  93  units  in  length  as  com- 
pared with  137  for  fuscipappa)  and  it  was  shown  in  Mann  (1925) 
that  considering  chromosome  size  alone  it  might  have  been  derived 
from  tectorum  (Eucrepis)  by  cross-division  of  all  chromosomes.  How- 
ever, these  two  species  are  so  widely  different  morphologically  that 
such  a  derivation  seems  hardly  possible.  On  account  of  the  strongly 
flattened  fruits  in  japonica.  (cf.  fig.  6,  v.  v'),  together  with  the  other 
differences  noted  in  Hoffmann's  key  and  the  small  size  of  the  chromo- 
somes, one  may  advocate  the  recognition  of  Cassini's  Youngia  as  a 
genus  intermediate  between  Crepis  and  Lactuca.  Cassini  (1831)  in 
the  original  diagnosis  of  Youngia  states:  "fruits  oblong,  more  or  less 
flattened,  .  .  .  absolutely  beakless"  .  .  .  [genus]  "not  to  be  con- 
founded with  Crepis  because  of  the  flattened  fruits."  Further  com- 
parative study  of  shape  of  fruits  and  size  of  chromosomes  will  be 
necessary,  however,  before  a  final  conclusion  can  be  drawn. 


1920)  Babcock-Leslcy :  Chromosomes  and  Taxonomic  Relationships  329 


TABLE   2 

Tentative   Classification   of   Twenty-one   Species   of   Crepis,   Arranged    for 
Comparison  with  Hoffmann's  Classification  Shown  in  Table  1 

B.  Pappus  bristles  longer. 

1.  Inner  or  all  the  fruits  long-beaked. 

2.  Fruits  large,  the  inner  ones  10-18  mm.  long. 
See.  II.  Anisoderis. 

C.  alpina,  foetida,  rubra  (figs.  1  and  2). 
2*.  Fruits  small,  the  inner  ones  5-7  mm.  long. 
3.  Fruits  all  similar. 
See.  III.  Barkhausia. 

C.  bursifolia,  sctosa,  iaraxacifolia  (fig.  3,  d,  e,  g). 

3*.  Fruits  of  two  shapes,  the  marginal  ones  winged. 
Sec.  IV.  Nemauchenes. 
C.  as  per  a  (fig.  3,  h,  h'). 
1*.  Fruits  reduced  at  apex,  but  not  beaked  or  only  short-beaked. 

4.   Inner    involucral    bracts    conspicuously    thickened    or    hardened    in 
fructiferous  heads. 
Sec.  V.   (Gatyona,  Cymboseris,  Phaecasium.) 
C.  Dioscoridis,  palaestina,  pulchra  (fig.  4). 

4*.  Inner  involucral  bracts  not  much  thickened  or  hardened  in  fructi- 
ferous heads. 
5.  Inner  involucral  bracts  more  or  less  spongy-thickened  dorsally. 
Sec.  VI.  Eucrepis. 

C.  capillaris,  parviflora  neglecta,  tectorum,  biennis,  montana  (fig.  5). 
5*.  Inner  involucral  bracts  little  or  not  at  all  changed. 
6.  Heads  small,  florets  few,  small. 
Sec.  VII.  Youngia. 
i,  C.  japonica  (fig.  6,  v,  v'). 

6*.  Heads  large,  florets  numerous,  large. 

7.  Plant  short-stemmed,  scapigerous,  scapes  1-headed,  rarely 
2-3  headed. 
8.  Rootstock  stoloniferpus,  forming  tubers. 
Sec.  VIII.  Aetheorrhiza. 
C.  bulbosa  (fig.  6,  u.) 

8*.  Rootstock   simple,   non-tuberous. 
Sec.  IX.  Omalocline. 
(  C.  aurea  (fig.  6,  w). 

7*.  Plant   long-stemmed,   erect,   foliate. 
Sec.  X.  Soyeria. 

C.  sibirica,  blaitarioides  (fig.  6,  x;  fig.  7,  y). 

Section  XI,  Catonia,  is  defined  by  Hoffman  as  including  species 
of  at  least  two  distinct  groups,  Omalocline  Cass,  and  Soyeria  Mann., 
represented  among  our  species  by  aurea  on  the  one  hand  and  by 
blaitarioides  and  sibirica  on  the  other.  In  other  words,  he  has  used 
an  ill-defined  genus  (Moench,  1794)  as  a  catchall  for  species  not 
already  assigned  to  sections.  This  would  be  more  evident  if  we  were 
considering  a  larger  number  of  species.     Furthermore,  blattarioides 


( 


330 


University  of  California   Publications  in  Agricultural  Sciences      [Vol.2 


and  sibirica,  although  somewhat  similar  in  both  habital  and  fruit 
characters  (see  figs.  6.  7),  are  very  distinct  from  each  other  in  many 
respects  and  have  the  same  general  native  and  distributional  habitats, 
all  of  which  would  indicate  that  they  are  not  closely  related  species. 
The  three  species  of  Catonia  studied  differ  greatly  cytologically. 
Aurea  (N  =  5)  is  rather  different  in  individuality  from  the  other 
species  with  5  pairs.  Blattarioides  (N  =  4)  has  a  chromosome  group 
much  like  that  of  tectorum,  while  sibirica  has  .">  pairs  of  very  large 
chromosomes  resembling  those  of  Dioscoridis,  puichra,  and  palaestina. 
Three  other  species  in  this  section  have  been  counted  recently,  but  as 
no  measurements  have  yet  been  made,  they  arc  not  included  in  table  3 
(see  p.  331). 

TABLE   3 

Tabulation  of  Twenty-one  Species  of  Crepia  A.cc6rding  to  a  Tentative  New 

Taxonomic  Grouping  and  with  Reference  i<>  Ni  mber  and  Length  of 

Chromosomes.    (The  Lexuth  Values  Represent  Averages 

from  Tex  Differext  Cells.) 


Number  of  Chromosome  Pairs 


Sec.  II     Anisoderis 

nl  inn, i 
ioi  tula 
rubra 
Sec.  Ill     Barkhausia 

bursi  folia 
8<  tOSQ 

taraxacifolia 
Nemauchenes 


S,T       IV. 

Sec,  V.* 
Sec.  VI. 


Sec.  VII 
Sec.  VII 
Sec.  IX. 
Sec.  X. 


aspera 


Dioscoridis 
palaestina 
puichra., 
Eucrepis 
capillaris 

parviflora 

tectorum 

montana 

'</•  iinis 

Youngia 
japonica  -. 
I.    Aetheorrhiza 

bulbosa 

Omalocline 

a  an  a 

Soyeria 

sibirica 
blattarioides. 


26 
25 
29 

.'I 
22. 
26    l 

23  '.< 

35  (i 
:u  l 
36.7 

26.2 

2.-,  :i 

28     I 

26.8 
(20 

15.7 

13.9 

21   0 

41.9 
29.0 


21.3 
20.8 
23.9 

22.0 

17  8 
23  :i 

21   :, 

29.3 

27  I) 
30.6 

20.4 
20  ."■ 
23.2 
21.4 

13  ■"> 

12  8 

18.0 

32.4 
23.8 


1  1  7. 
17   7 

is  :, 

in  ;. 

i  i  n 

21    2 

19.7 

24.9 
24.6 

2.".   :> 

I  1  8 
It  I 
20.2 

17   7 


12   2 

12    1 

16.2 

27.6 
20.6 


13.  1 

l.-,  8 

16  2 

12   7 
'.'.  1 

17  s 

1 7  :» 

19  3 
21  2 
19.3 


17.2 
16.0 


11.5 

11    7 
15.  1 

23.2 

17   7 


12  2 

1  1    I 

1  I   'i 


I  A  .  2 

10.8 

II  1 
L3  2 

is  :, 


12   .". 

Ill   (I 
1(1   (', 


9.7 

Id  1 


'.I    2 
9.6 


S    li 


*Gatyona,  Cymboseris,  and  Phaecasium  combined. 

t  Not  measured;  size  range  much  like  that  of  species  in  this  group. 


L926] 


Bdbcock— Lesley :  Chromosomes  and  Taxonomic  Relationships 


33] 


Our  analysis  of  relationships  among  these  twenty-one  species,  as 
based  on  comparative  morphology,  is  summarized  in  table  2.  This 
analysis  is  presented  only  in  a  tentative  way,  as  an  aid  in  the  study  of 
eytologicaJ  evidence  and  a  step  toward  the  classification  of  the  entire 
genus. 

The  correspondence  of  the  new  taxonomic  grouping  with  chromo- 
some number  and  size  is  shown  in  table  .'{. 

Since  the  foregoing  was  written,  the  chromosomes  have  been 
examined  in  the  following  additional  species  of  Crepis.  The  classifica- 
tion into  sections  is  according  to  the  tentative  new  arrangement  shown 
in  tables  2  and  3. 

IV.     Nemauchenes 
C.  amplexifolia  (Godr.)  Willk N=  4      size  medium 

VI.  Eucrepis 

C.  hjrata  Froel N=   6      size  medium 

C.  mollis  (Jacq.)  Asch N=  6      size  medium 

C.  pygmaea  L N=  6      size  medium 

C.  chondrilloides  Jacq N=  4      size  large 

C.  Blavii  Asch N=  4      size  large 

C.  ciliata  C.  Koch N  =  20      size  medium 

VII.  Youngia 

C.fuscipappa  (Thw.)  Bent ,h N=   8      size  medium 

IX.  Omalocline 

C.  Hookeriana  Ball N=  4      size  medium 

X.  Soyeria 

C.  conyzaefolia  (Gouan)  Dalla  Torre N=   4      size  large 

C.  tingilana  Salz.  ex  Ball N=   5      size  medium 

C.  paludosa  (L)  Mnch N=  6      size  large 

With  reference  to  the  six  species  classified  under  Eucrepis,  the  first 
group  of  three  lyrata,  mollis,  and  pygmaea,  must  be  grouped  with 
montana  on  the  basis  of  morphology,  and  they  have  similar  chromo- 
somes. The  next  two,  chondrilloides  and  Blavii,  represent  a  subdivision 
of  Eucrepis  not  previously  studied  and  are  very  distinct  from  other 
members  of  Eucrepis.  Lastly  ciliata  is  certainly  in  Eucrepis,  and  its 
chromosomes  indicate  relationship  to  biennis,  to  which  species  there  is 
considerable  resemblance  in  the  rosettes  of  our  immature  plants. 
Evidently  Eucrepis  is  too  heterogeneous  a  group  to  be  retained  as  a 
section,  and  in  the  taxonomic  revision  of  the  genus  which  is  now  in 
preparation  it  will  become  a  subgenus  containing  several  sections. 


332  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  2 

It  is  evident  that,  generally  speaking,  there  is  a  definite  correspond- 
ence between  the  taxonomic  position  of  the  species  studied  and  their 
chromosome  number  and  especially  with  chromosome  size,  and  that  the 
new  taxonomic  grouping  increases  this  correspondence.  It  is  almost 
perfect  in  Section  II,  and  in  Section  III  (cf.  table  3),  and  the  species 
that  stand  apart  in  the  classification  also  differ  markedly  from  the  rest 
in  either  size  or  number  of  chromosomes  (Sections  V.  VI,  and  VII). 
It  will  be  noted  that  Section  III  and  Section  VI  contain  species 
will)  similar  chromosome  numbers  and  sizes,  parviflora  and  setosa 
having  very  similar  size  differences,  as  do  also  twraxacifdlia  and 
tectorum.  It  would  seem  worth  while  to  test  these  groups  by  means 
of  species-hybridization.  Sections  VII  and  VIII  as  compared  with 
Sections  V  and  X  exhibit  the  most  extreme  differences  in  chromosome 
size. 


LITERATURE  A XI)   DISCUSSION 

The  numerous  summaries  of  chromosome  numbers  which  have 
appeared  in  recent  years  clearly  indicate  that  there  is  some  parallelism 
between  chromosome  number,  size,  and  shape  and  relationship  in  the 
plant  and  animal  kingdoms.  In  general,  members  of  the  same  genus 
usually  have  similar  chromosome  numbers.  In  the  Liliaceae,  for 
instance,  each  genus  has  a  characteristic  number  of  chromosomes.  On 
the  other  hand,  in  wheat,  instead  of  exact  numerical  correspondence 
within  the  genus,  the  species  fall  into  three  groups  with  respect  to 
chromosome  number  (Sakamura.  1918),  einkorn  having  7,  emmer  14. 
and  vulgare  21  pairs  of  chromosomes.  These  groups  also  differ  from 
one  another  in  susceptibility  to  rust,  serological  relations,  and 
morphology  (Sax,  1921).  Thus  in  the  genus  Triticum  the  most  similar 
species  are  most  alike  in  chromosome  number.  Winge  (1!)17,  pp.  166- 
168)  cites  an  interesting  case  from  the  Compositae.  Species  were 
described  as  having  8,  9,  14,  16,  18,  24,  27,  32,  36,  and  4.">  pairs.  When 
these  species  were  classified  by  tribes,  the  numbers  formed  two  series 
with  8  as  the  ground  number  for  the  Ileliantheae.  and  9  for  the 
Anthemideae.  Marchal  (1920)  recently  noted  that  the  species  of  the 
genus  Campanula  which  belong  to  the  section  .Medium  have  X  values 
of  17,  34,  or  .31,  but  finds  that  the  other  section  of  the  genus  fails  to 
show  a  similar  numerical  seriation,  including  such  X  values  as  8,  10. 
and  13.  He  suggests  (p.  66)  that  "The  results  of  the  cytological  study 
of  species  of  section  II  [Rapunculus]  tend  to  show  that  this  grouping 
is  much  less  natural  and  less  homogeneous  than  the  preceding." 


1920]  Babcock— Lesley :  Chromosomes  and  Taxonomic  "Relationships  333 

McClung  (1908),  on  the  basis  of  observations  on  many  genera  of 
Orthoptera,  says, 

Merely  as  :i  result  of  the  study  I  have  made  of  the  germ  cells  I  would  have 
classified  these  insects  into  two  groups,  one  having  a  complex  of  twenty-three 
chromosomes  and  the  other  of  thirty-three.  On  the  other  hand,  many  taxo- 
nomists,  from  careful  and  minute  examination  of  the  external  anatomy  of  these 
same  species,  had  agreed  in  placing  them  into  family  groups  which  they  call 
the  Acrididae  and  Locustidae. 

McClung  (1917)  has  made  an  especially  thorough  study  of  the  genera 
Hcsperotettix  and  Mermiria,  and  lias  had  the  benefit  of  the  cooperation 
of  experts  on  the  classification  of  the  Orthoptera,  with  similar  results. 

Metz  (1914,  1916)  has  shown  that  the  Drosophilidae  have  rather 
similar  chromosomes  and  that  the  species  form  several  groups  on  the 
basis  of  their  cytological  characteristics.  Metz  and  Lancefield  (1922) 
state  that  the  13  species  belonging  to  class  A,  of  which  D.  melanog  aster 
is  an  example,  are  scattered  throughout  the  genus.  The  Drosophilidae 
are  of  especial  interest  from  the  standpoint  of  cytology  and  taxonomy, 
since  something  is  known  of  the  arrangement  of  genes  within  the 
chromosomes  of  several  species,  and  it  is  therefore  possible  to  com- 
pare the  chromosomes  from  a  genetical  as  well  as  a  purely  morpho- 
logical viewpoint.  Sturtevant  (1921)  says,  "44  recessive  mutant 
genes  in  41  loci  of  D.  melanogaster  and  12  recessive  mutant  genes 
of  D.  simulans  (in  12  loci)  are  also  recessive  in  melanog  aster-simulams 
hybrids."  Some  of  these  genes  are  found  in  each  of  the  4  chro- 
mosomes indicating  that  "The  data  from  D.  simulans  show  what 
was  suggested  by  the  other  results  and  by  much  cytological  data,  that 
the  constitution  of  a  chromosome  may  be  essentially  the  same  in  two 
different  species. ' '  Both  of  these  species  belong  to  type  A  cytologically 
(Metz  and  Moses,  1923)  and  are  closely  related  taxonomically.  The 
evidence  from  I),  obscura  and  D.  willistoni,  on  the  other  hand,  shows 
that  the  chromosomes  which  one  would  naturally  suppose  to  be 
identical  on  the  basis  of  purely  cytological  criteria  are  not  the  same 
genetically,  since  Metz  and  Lancefield  (1922)  state:  "In  the  two 
species  having  V-shaped  X  chromosomes,  then,  yellow  and  scute  are 
'located'  near  the  middle  of  the  chromosome  map,  while  in  melano- 
gaster with  its  short  rod-like  X  chromosome,  yellow  and  scute  are  on 
one  end."  Metz  and  Moses  (1923)  emphasize  the  importance  of 
genetical  evidence  in  any  attempt  to  evaluate  the  significance  of 
similarities  or  differences  of  a  cytological  type. 

Lists  of  chromosome  numbers  also  contain  what  appear  to  be  many 
flagrant  exceptions  to  the  view  that  the  species  of  a  genus  will  be  cyto- 


334  University  of  California  Publications  in  Agricultural  Sciences      [Vol.2 

logically  similar.  In  fact,  the  summaries  of  Ishikawa  (1916)  and 
Tischler  (1916,  1922)  contain  very  few  genera  with  either  the  same 
number  throughout,  or  even  a  single  ground  number.  Even  in  the 
Liliaceae  certain  species  have  been  reported  as  having  chromosome 
numbers  different  from  that  typical  of  the  genus.  Time  and  further 
work  alone  will  tell  how  many  of  these  exceptions  are  real  and  how 
many  are  due  to  error.  At  present  few  genera  have  been  much  studied, 
and  even  where  a  large  number  of  counts  have  been  published,  the  same 
error  may  appear  in  a  whole  series  of  observations.  For  instance,  in 
both  Triticum  and  Rosa  numerous  species  were  included  in  recent 
summaries  as  having  8  and  16  pairs  of  chromosomes.  Il  has  been 
shown  by  Sakamura  (1918)  and  Sax  (1918,  1921)  for  Triticum,  and 
by  Tiickholm  (1922)  for  Rosa,  that  7  and  not  S  is  the  ground  number 
for  both  genera.  Another  very  real  source  of  error  in  any  attempt  to 
generalize  from  summaries  lies  in  the  fact  that  few  eytologists  are 
trained  taxonomists.  Our  experience  with  Crepis  indicates  thai  seeds 
which  are  obtained  from  the  most  reputable  sources  may  be  incorrectly 
labeled,  and,  unless  the  seeds  are  grown  and  the  plants  classified,  we 
cannot  always  be  positive  that  they  even  belong  to  that  genus,  much  less 
to  the  species  to  which  the  sender  has  attributed  them.  While  lists  of 
chromosome  numbers  include  such  errors  as  are  indicated  above  and 
are,  therefore,  not  suitable  as  a  basis  for  very  sweeping  generalization, 
no  one  can  doubt  that  chromosome  number  and.  in  some  cases,  size  and 
shape,  are  good  specific  characters.  We  venture  the  prediction  that 
chromosome  number  and  size  will  sometime  lie  given  with  taxonomic 
descriptions. 

Crepis  contains  species  with  3.  4.  5,  6,  8,  9,  and  20  pairs  of  chromo- 
somes; but  3,  6,  8,  9,  and  20  are  much  less  frequent  numbers  than  4 
or  5,  each  of  the  former  characterizing  only  one  of  the  twenty-one 
species  represented  in  table  3.  A  similar  condition  has  been  described 
for  a  closely  related  genus,  Lactuca  (Ishikawa,  1921),  most  of  the 
species  having  5,  8,  9,  or  12  as  the  haploid  number,  while  single  species 
have  7,  16,  or  24.  It  is  especially  interesting  that  Ishikawa  finds  that 
his  grouping  of  species  according  to  chromosome  number  and  size  cor- 
responds very  strikingly  with  the  taxonomic  classification  of  Nakai 
(1920).  In  Lactuca,  as  in  Crepis,  great  differences  in  chromosome 
size  exist,  and  because  of  this  and  the  numerical  differences,  Ishikawa 
is  inclined  to  think  that  Lactuca  is  really  an  assemblage  of  genera. 
It  is  particularly  interesting  that  two  varieties  of  L.  dentata  have  12 
pairs,  while  one  has  7  pairs  of  chromosomes. 


1926]         Bdbcock— Lesley :  Chromosomes  <nt<t  Taxonomic  Relationships  335 

Crepis  senecwides  Delile,  a  native  of  Egypt,  is  a  species  of  peculiar 
interest  because  its  fruit  is  definitely  flattened,  although  not  so  much 
so  as  in  the  more  extreme  types  of  Lactuca,  and  it  lacks  the  thin  lateral 
margin  (fig.  3,  /,  /'),  while  on  the  basis  of  its  involucre,  number  of 
florets  per  head,  and  habit  it  does  not  fit  into  any  of  the  sections  of 
Lactuca  provided  by  Hoffmann  in  the  Pflanzenfamilien.  Further- 
more, it  has  four  pairs  of  small  chromosomes  and  produces  sterile 
hybrids  when  crossed  with  C.  parvifiora  and  C.  vesicaria.  Thus  we 
find  fairly  close  relationship  between  what  simulates  Lactuca  in  achene 
shape  and  certain  species  of  Crepis.  This  evidence  is  not  unique,  how- 
ever, as  there  are  other  points  at  which  the  two  genera  meet.  Nakai. 
for  example,  found  it  necessary  to  choose  between  the  alternatives  of 
either  recognizing  Ixeris,  Paraixeris,  and  Crepidiastrum  as  distinct 
genera  or  combining  Crepis  and  Lactuca.  For  the  present,  we  are 
inclined  to  consider  C .  senecioides  as  Crepis,  but  it  is  highly  desirable 
that  critical  comparison  of  the  fruits  be  made  between  senecioides  and 
similar  Crepis  species  as  well  as  between  senecioides  and  the  North 
African  species  of  Lactuca,  and  that  chromosome  counts  of  the  latter 
be  obtained.  We  have  indicated  one  such  comparison  in  the  drawing 
of  C.  bursifolia  (fig.  3,  g,  g'). 

A  group  of  forms  which  have  usually  been  treated  as  distinct 
species,  viz.,  Crepis  vesicaria  L.,  C.  ta/raxadfolia  Thuill.,  C.  Marschallii 
F.  Schultz,  and  C.  myriocephala  Coss.  et  DR.,  may  be  considered  as 
one  species  for  the  following  reasons:  (1)  They  are  closely  similar 
morphologically,  and  their  close  relationship  has  been  recognized  by 
several  taxonomists.  (2)  They  have  nearly  identical  chromosome 
groups.  (3)  They  intercross  freely  and  produce  highly  fertile  hybrids. 
That  these  should  be  considered  as  subspecies  of  one  species  rather  than 
as  varieties  is  indicated  by  the  following  facts:  (1)  All  except  one. 
taraxacifolia,  which  is  probably  the  oldest  phylogenetically,  occupy 
distinct  geographic  areas.  (2)  All  are  highly  variable,  and  taraxaci- 
folia is  really  polymorphous.  However,  as  no  changes  in  nomenclature 
are  proposed  in  the  present  paper,  we  shall  continue  to  use  the 
binomials  in  what  follows. 

A  summary  of  the  data  recently  presented  by  Bleier  (1925)  and 
Karpetchenko  (1925)  shows  that  in  Trifolium  section  Chronosemium* 


*  Greene  (1897)  discusses  at  length  the  evidence  for  retaining  the  genus 
Chrysaspis  instead  of  treating  it  as  a*  section  (Chronosemiiun)  of  Trifolium. 
He  says:  ''And  since  Linnaeus'  time  there  have  been  a  number  of  open  protests, 
and  by  most  able  botanists,  against  the  treating  of  the  Hop  Trefoils  as  con- 
generic with  such  plants  as  Trifolium  pratense  and  its  allies.  Systematists  of 
no  less  renown  than  Lamarck  and  Desfontaines  referred  the  plants  to  Melilotus 
rather  than  Trifolium." 


336  Universitj/  of  California  Publications  in  Agricultural  Sciences      [Vol.  '2 

contains  species  with  7  or  14  pairs  of  chromosomes,  while  Enamoria 
and  Galearia  consist  of  species  with  8  or  16  pairs,  except  for  T. 
glomeratum  which  has  7  pairs;  whereas  Lagopus  contains  species  with 
7,  8  or  a  large  number  of  pairs,  possibly  48-49.  Bleier  presents  some 
evidence  that  differences  in  nuclear  volume  and  in  chromosome  size 
occur  in  the  genus.  The  cases  of  Trifolmm,  Campanula,  Lactiica,  and 
Crepis  are  alike  in  that,  while  many  correspondences  have  been  found 
between  chromosome  number  and  classification,  some  exceptions  still 
exist  which  require  further  study.  Even  within  Eucrepis,  however, 
which  shows  a  remarkable  diversity  of  chromosome  numbers,  morpho- 
logical resemblances  appear  within  the  section  which  are  correlated 
with  similarity  of  chromosome  number  and  size. 

In  the  genus  Seneeio,  At'zelius  (1924)  reports  a  high  degree  of 
homogeneity  within  the  genus  as  indicated  by  close  conformity  to  the 
numerical  series,  5,  10,  20,  30;  also  in  most  of  the  sections,  ;is  only  one 
of  the  eight  sections  contains  species  of  different  numerical  rank. 
However,  as  the  species  he  lias  studied  are  mostly  from  the  Old  "World, 
the  situation  within  the  genus  as  a  whole  may  yet  be  found  to  differ 
considerably. 

In  Carex,  Heilborn  (1924)  has  recently  reported  thai  species  exist 
with  9,  15,  16,  19,  24,  26,  27,  28,  29,  31,  32,  33,  34.  35,  36.  37,  38,  40. 
41,  42.  and  56  as  haploid  numbers.  Related  species  show  some  num- 
erical similarity,  although  this  is  by  no  means  so  striking  as  in  Lactuca. 

('reins  also  contains  a  series  of  chromosome  numbers  like  that 
reported  for  Carer,  3,  4,  5,  6,  8,  9,  and  20  pairs.  Most  of  the  species 
with  3,  4,  5,  6,  and  20  pairs  have  chromosomes  similar  in  size,  although 
some  4-  and  5-paired  species  have  chromosomes  that  are  much  larger 
than  is  usual  in  Crepis,  in  so  far  as  it  has  been  studied  cytologically. 
Two  of  the  three  species  which  we  have  found  with  S  and  9  pairs 
have  much  smaller  chromosomes  than  is  usual  in  the  genus.  It  was 
noted  above  that  the  section  Youngia  might  be  removed  from  Crepis. 
If  this  is  done  we  shall  lack  species  with  8  pairs.  It  is  noteworthy 
that  Eucrepis  contains  species  with  3,  4,  5,  6,  and  20  pairs.  Navashin 
(1925&)  and  Collins  and  Mann  (1923)  found  evidence  that  polyploidy 
occurs  in  Crepis,  but  it  was  pointed  out  by  Mann  (1925)  that  some 
other  type  of  chromosome  multiplication  must  account  for  the  origin 
of  most  of  the  species  which  we  have  studied.  Non-disjunction  was 
first  suggested  as  a  source  of  the  chromosome  differences  observed  by 
Rosenberg  (1918)  ;  and,  whereas  this  cannot  account  for  all  the  differ- 
ences, it  may  be  the  most  important  factor.     In  any  case  it  certainly 


-\ 


l!i2(i|  Bab  cock—Lesley :  Chromosomes  and  Taxonomic  Relationships  3.37 

is  the  most  probable  method  which  we  know  occurs.  Tt  should  be 
emphasized  in  all  such  discussion,  however,  that  there  is  no  known  case 
of  a  stable  combination  of  chromosomes  which  has  been  observed  to 
originate  in  this  way.  Similarly,  no  case  of  changed  individuality  of 
the  chromosomes  which  would  account  for  stable  types  like  C.  setosa, 
neglecta,  and  parviflora  has  been  reported  to  have  occurred  experi- 
mentally. Chromosome  fragmentation  is  known  to  occur  following 
trisomy,  but  whether  such  types  ever  become  stabilized  with  a  pair  of 
fragments  added  to  the  normal  specific  complex,  or  whether  a  chromo- 
some complex  can  lose  a  considerable  section  of  a  pair  of  chromosomes 
and  the  plants  lacking  this  part  be  viable  and  fertile,  is  unknown.  Our 
strain  of  C.  MarschaJlii  is  peculiar  in  that,  when  we  obtained  it,  certain 
plants  contained  9  chromosomes  in  the  root-tip  cells,  comprising  the 
usual  complex  for  the  vesicaria  group  of  species  plus  a  very  short 
unpaired  chromosome.  The  source  of  this  small  extra  chromosome  is 
quite  uncertain,  although  it  is  known  to  be  an  addition  to  the  complex. 
Navashin  (1925)  presented  a  figure  of  C.  Marschalh'i  that  is  like 
vesicaria  and  lacks  the  small  chromosome.  Some  of  our  9-chromosome 
MarschaJlii  plants  were  very  fertile,  and  among  their  progeny  one  at 
least  has  two  such  small  chromosomes.  This  matter  is  being  studied 
further  and  will  be  reported  upon  separately.  Should  such  a  plant  be 
fertile,  we  might  understand  how  such  differences  in  chromosome 
groups  could  arise  in  a  genus. 

Navashin  (192;k/)  has  emphasized  the  importance  of  minute 
"Traibanten"  or  satellites  attached  to  the  tips  of  certain  chromosome 
pairs  in  Crepis  species.  He  believes  that  shape  of  chromosome  and  the 
presence  or  absence  of  satellites  is  "weit  wichtiger  fur  die  Charakter- 
istiJe  des  Kernes  bzw.  der  Art,  als  die  Zahl  der  Chromosomal  u nd  deren 
Dimensioiien  siud."  He  groups  together  in  class  " D  "  all  chromosomes 
having  satellites  although  in  C.  Dioscoridis,  one  of  19  length  units  bears 
the  satellite,  while  in  C.  parviflora:  he  finds  it  upon  one  of  about  10 
length  units.  But  in  our  material,  which  was  fixed  in  C.  A.  U., 
Trabanten  were  not  always  present,  and  sometimes  resembled  the 
strands  and  masses  of  nucleolar  material  which  are  frequently  found 
being  extruded  from  the  chromosome  plate.  Consequently  size,  which 
is  relatively  far  less  variable  and  more  easily  evaluated,  was  selected 
as  the  best  criterion  of  relationship,  and  it  has  thus  far  proved  a  very 
good  one  as  tested  by  species-hybridization.  That  shape  relationships 
may  help  in  differentiating  two  pairs  of  chromosomes  of  the  same  size 
in  certain  species  of  Crepis  is  clearly  indicated  by  Navashin 's  figures, 


338  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  2 

but  the  relative  importance  of  size  and  shape  as  indicators  of  relation- 
ship between  species  can  be  tested  only  by  species-hybridization  and 
genetic  analysis.  Probably  both  modes  of  attack  will  sometime  prove 
useful,  but  thus  far  they  have  not  given  us  clues  to  relationship  which 
could  not  be  determined  by  comparative  length  alone.  Our'  material, 
like  that  of  Navashin,  shows  Trabanten  attached  to  the  shortest  chro- 
mosome in  both  tectorum  and  Marsckallhi,  species  which  are  widely 
separated  in  all  classifications.  This  is  very  disappointing,  since  one 
might  have  hoped  that  they  could  be  differentiated  thereby.  It  seems 
evident  from  our  studies  that  if  Navashin  were  to  make  comparative 
measurements  of  the  chromosomes,  he  might  change  his  estimate  of  the 
chromosome  homologies  in  the  species  which  he  studied. 

Corrections  in  Nomenclature  in  Part  I 

In  the  preceding  paper   (Mann,  1925),  the  following  corrections 
should  be  made : 

For  breviflora  Delile  read  senecioides  Delile. 

For  grtmdiflora  Tausch  read  cony  zae  folia  (Gouan)  Dalla  Torre. 

For  Sieberi  Boissier  read  montana  d'Urville. 


SUMMARY  AND  CONCLUSIONS 

1.  Taxonomically  considered,  the  genus  Crepis,  as  it  stands  at 
present,  is  a  heterogeneous  assemblage  of  distinct  but  related  groups  of 
species.  The  sections  recognized  by  Hoffmann  and  their  classification 
by  him  are  not  wholly  satisfactory  on  the  basis  of  comparative  morph- 
ology alone.  A  more  satisfactory  classification  of  the  species  under 
consideration,  which  reduces  the  sections  from  eleven  to  ten  and 
regroups  certain  species,  is  suggested,  and  the  cytological  evidence  is 
considered  in  relation  to  the  new  grouping. 

2.  From  the  standpoint  of  cytology  as  well,  the  genus  Crepis  must 
be  considered  as  heterogeneous.  Similarity  of  chromosome  size  seems 
to  be  a  better  criterion  of  relationship  than  number  alone,  although 
closely  related  species  usually  have  the  same  numbers  of  chromosomes. 
Most  of  the  cytological  heterogeneity  is  confined  to  the  sections 
Eucrepis  and  Catonia  of  Hoffmann's  classification.  The  former  is 
found  to  be  too  heterogeneous  both  taxonomically  and  cytologically 
to  be  retained  as  a  section,  and  certain  new  subgroupings  are  needed 
within  it.  Catonia  also  requires  some  drastic  changes.  It  is  hoped 
that  further  study  will  reveal  natural  subgroups  within  Catonia;  also 


1926]  Babcock— Lesley:  Chromosomes  and  Taxonomie  Relationships  339 

1  luit  it  may  throw  light  on  the  origin  of  chromosomal  differences  in 
Crepis.  Further  research  on  species  hybrids  is  in  progress  and  should 
throw  considerable  light  on  problems  of  relationship  within  the  genus. 

3.  Differences  in  chromosome  dimensions  are  found  among  the 
species  of  this  genus.  We  note  especially  (a)  differences  in  size  of  all 
the  chromosomes;  (b)  similarity  in  size  of  most  of  the  chromosomes 
and  differences  in  others.  If  Youngia  be  omitted,  there  remains  only 
one  species,  C.  bulbosa,  having  all  the  chromosomes  smaller  than  is 
usual  for  the  genus.  At  present  we  have  this  species  in  a  section  by 
itself,  but  its  ultimate  classification  awaits  further  study.  Of  the  three 
species  of  type  (6),  in  which  certain  chromosomes  are  much  shorter 
than  is  usual  in  the  genus  and  the  others  are  similar  in  size,  C.  negiecta 
and  C.  parviflora  are  provisionally  classified  in  Eucrepis,  while  C. 
setosa  is  in  Barkhausia. 

4.  It  is  noted  that  certain  species  having  similar  chromosome  sizes, 
particularly  C.  tectorxim  and  the  vesicaria  group  (including  taraxaci- 
folia,  Marsrhallii,  and  myriocephala) ,  are  classed  respectively  in 
Eucrepis  and  Barkhausia.  These  facts  may  indicate  either  close 
relationship  between  the  two  sections  or  that  similar  changes  in  the 
chromosomes  have  taken  place  independently  in  the  two  groups.  For 
the  present  we  favor  the  latter  assumption. 

5.  This  study  was  undertaken  partly  for  the  purpose  of  testing  the 
cyto-taxonomic  method  in  a  genus  favorable  for  such  research.  As  the 
work  progresses  we  are  becoming  more  and  more  impressed  with  the 
value  of  this  method,  and  it  is  our  intention  to  extend  it  to  include 
as  many  species  of  Crepis  as  can  be  obtained  and  cultivated  at 
Berkeley. 

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